kernel - Fix bottlenecks that develop when many processes are running

[dragonfly.git] / sys / vm / vm_page.c

/*
 * Copyright (c) 1991 Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * The Mach Operating System project at Carnegie-Mellon University.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from: @(#)vm_page.c     7.4 (Berkeley) 5/7/91
 * $FreeBSD: src/sys/vm/vm_page.c,v 1.147.2.18 2002/03/10 05:03:19 alc Exp $
 */

/*
 * Copyright (c) 1987, 1990 Carnegie-Mellon University.
 * All rights reserved.
 *
 * Authors: Avadis Tevanian, Jr., Michael Wayne Young
 *
 * Permission to use, copy, modify and distribute this software and
 * its documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 *
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
 * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 *
 * Carnegie Mellon requests users of this software to return to
 *
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 *
 * any improvements or extensions that they make and grant Carnegie the
 * rights to redistribute these changes.
 */
/*
 * Resident memory management module.  The module manipulates 'VM pages'.
 * A VM page is the core building block for memory management.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/proc.h>
#include <sys/vmmeter.h>
#include <sys/vnode.h>
#include <sys/kernel.h>
#include <sys/alist.h>
#include <sys/sysctl.h>
#include <sys/cpu_topology.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.h>
#include <vm/vm_kern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_object.h>
#include <vm/vm_page.h>
#include <vm/vm_pageout.h>
#include <vm/vm_pager.h>
#include <vm/vm_extern.h>
#include <vm/swap_pager.h>

#include <machine/inttypes.h>
#include <machine/md_var.h>
#include <machine/specialreg.h>

#include <vm/vm_page2.h>
#include <sys/spinlock2.h>

/*
 * SET - Minimum required set associative size, must be a power of 2.  We
 *       want this to match or exceed the set-associativeness of the cpu.
 *
 * GRP - A larger set that allows bleed-over into the domains of other
 *       nearby cpus.  Also must be a power of 2.  Used by the page zeroing
 *       code to smooth things out a bit.
 */
#define PQ_SET_ASSOC            16
#define PQ_SET_ASSOC_MASK       (PQ_SET_ASSOC - 1)

#define PQ_GRP_ASSOC            (PQ_SET_ASSOC * 2)
#define PQ_GRP_ASSOC_MASK       (PQ_GRP_ASSOC - 1)

static void vm_page_queue_init(void);
static void vm_page_free_wakeup(void);
static vm_page_t vm_page_select_cache(u_short pg_color);
static vm_page_t _vm_page_list_find2(int basequeue, int index);
static void _vm_page_deactivate_locked(vm_page_t m, int athead);

MALLOC_DEFINE(M_ACTIONHASH, "acthash", "vmpage action hash");

/*
 * Array of tailq lists
 */
__cachealign struct vpgqueues vm_page_queues[PQ_COUNT];

LIST_HEAD(vm_page_action_list, vm_page_action);

/*
 * Action hash for user umtx support.  Contention is governed by both
 * tsleep/wakeup handling (kern/kern_synch.c) and action_hash[] below.
 * Because action_hash[] represents active table locks, a modest fixed
 * value well in excess of MAXCPU works here.
 *
 * There is also scan overhead depending on the number of threads in
 * umtx*() calls, so we also size the hash table based on maxproc.
 */
struct vm_page_action_hash {
        struct vm_page_action_list list;
        struct lock     lk;
} __cachealign;

#define VMACTION_MINHSIZE       256

struct vm_page_action_hash      *action_hash;
static int vmaction_hsize;
static int vmaction_hmask;

static volatile int vm_pages_waiting;
static struct alist vm_contig_alist;
static struct almeta vm_contig_ameta[ALIST_RECORDS_65536];
static struct spinlock vm_contig_spin = SPINLOCK_INITIALIZER(&vm_contig_spin, "vm_contig_spin");

static u_long vm_dma_reserved = 0;
TUNABLE_ULONG("vm.dma_reserved", &vm_dma_reserved);
SYSCTL_ULONG(_vm, OID_AUTO, dma_reserved, CTLFLAG_RD, &vm_dma_reserved, 0,
            "Memory reserved for DMA");
SYSCTL_UINT(_vm, OID_AUTO, dma_free_pages, CTLFLAG_RD,
            &vm_contig_alist.bl_free, 0, "Memory reserved for DMA");

static int vm_contig_verbose = 0;
TUNABLE_INT("vm.contig_verbose", &vm_contig_verbose);

RB_GENERATE2(vm_page_rb_tree, vm_page, rb_entry, rb_vm_page_compare,
             vm_pindex_t, pindex);

static void
vm_page_queue_init(void) 
{
        int i;

        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_FREE+i].cnt_offset =
                        offsetof(struct vmstats, v_free_count);
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_CACHE+i].cnt_offset =
                        offsetof(struct vmstats, v_cache_count);
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_INACTIVE+i].cnt_offset =
                        offsetof(struct vmstats, v_inactive_count);
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_ACTIVE+i].cnt_offset =
                        offsetof(struct vmstats, v_active_count);
        for (i = 0; i < PQ_L2_SIZE; i++)
                vm_page_queues[PQ_HOLD+i].cnt_offset =
                        offsetof(struct vmstats, v_active_count);
        /* PQ_NONE has no queue */

        for (i = 0; i < PQ_COUNT; i++) {
                TAILQ_INIT(&vm_page_queues[i].pl);
                spin_init(&vm_page_queues[i].spin, "vm_page_queue_init");
        }
}

/*
 * note: place in initialized data section?  Is this necessary?
 */
long first_page = 0;
int vm_page_array_size = 0;
vm_page_t vm_page_array = NULL;
vm_paddr_t vm_low_phys_reserved;

/*
 * (low level boot)
 *
 * Sets the page size, perhaps based upon the memory size.
 * Must be called before any use of page-size dependent functions.
 */
void
vm_set_page_size(void)
{
        if (vmstats.v_page_size == 0)
                vmstats.v_page_size = PAGE_SIZE;
        if (((vmstats.v_page_size - 1) & vmstats.v_page_size) != 0)
                panic("vm_set_page_size: page size not a power of two");
}

/*
 * (low level boot)
 *
 * Add a new page to the freelist for use by the system.  New pages
 * are added to both the head and tail of the associated free page
 * queue in a bottom-up fashion, so both zero'd and non-zero'd page
 * requests pull 'recent' adds (higher physical addresses) first.
 *
 * Beware that the page zeroing daemon will also be running soon after
 * boot, moving pages from the head to the tail of the PQ_FREE queues.
 *
 * Must be called in a critical section.
 */
static void
vm_add_new_page(vm_paddr_t pa)
{
        struct vpgqueues *vpq;
        vm_page_t m;

        m = PHYS_TO_VM_PAGE(pa);
        m->phys_addr = pa;
        m->flags = 0;
        m->pat_mode = PAT_WRITE_BACK;
        m->pc = (pa >> PAGE_SHIFT);

        /*
         * Twist for cpu localization in addition to page coloring, so
         * different cpus selecting by m->queue get different page colors.
         */
        m->pc ^= ((pa >> PAGE_SHIFT) / PQ_L2_SIZE);
        m->pc ^= ((pa >> PAGE_SHIFT) / (PQ_L2_SIZE * PQ_L2_SIZE));
        m->pc &= PQ_L2_MASK;

        /*
         * Reserve a certain number of contiguous low memory pages for
         * contigmalloc() to use.
         */
        if (pa < vm_low_phys_reserved) {
                atomic_add_int(&vmstats.v_page_count, 1);
                atomic_add_int(&vmstats.v_dma_pages, 1);
                m->queue = PQ_NONE;
                m->wire_count = 1;
                atomic_add_int(&vmstats.v_wire_count, 1);
                alist_free(&vm_contig_alist, pa >> PAGE_SHIFT, 1);
                return;
        }

        /*
         * General page
         */
        m->queue = m->pc + PQ_FREE;
        KKASSERT(m->dirty == 0);

        atomic_add_int(&vmstats.v_page_count, 1);
        atomic_add_int(&vmstats.v_free_count, 1);
        vpq = &vm_page_queues[m->queue];
        TAILQ_INSERT_HEAD(&vpq->pl, m, pageq);
        ++vpq->lcnt;
}

/*
 * (low level boot)
 *
 * Initializes the resident memory module.
 *
 * Preallocates memory for critical VM structures and arrays prior to
 * kernel_map becoming available.
 *
 * Memory is allocated from (virtual2_start, virtual2_end) if available,
 * otherwise memory is allocated from (virtual_start, virtual_end).
 *
 * On x86-64 (virtual_start, virtual_end) is only 2GB and may not be
 * large enough to hold vm_page_array & other structures for machines with
 * large amounts of ram, so we want to use virtual2* when available.
 */
void
vm_page_startup(void)
{
        vm_offset_t vaddr = virtual2_start ? virtual2_start : virtual_start;
        vm_offset_t mapped;
        vm_size_t npages;
        vm_paddr_t page_range;
        vm_paddr_t new_end;
        int i;
        vm_paddr_t pa;
        vm_paddr_t last_pa;
        vm_paddr_t end;
        vm_paddr_t biggestone, biggestsize;
        vm_paddr_t total;
        vm_page_t m;

        total = 0;
        biggestsize = 0;
        biggestone = 0;
        vaddr = round_page(vaddr);

        /*
         * Make sure ranges are page-aligned.
         */
        for (i = 0; phys_avail[i].phys_end; ++i) {
                phys_avail[i].phys_beg = round_page64(phys_avail[i].phys_beg);
                phys_avail[i].phys_end = trunc_page64(phys_avail[i].phys_end);
                if (phys_avail[i].phys_end < phys_avail[i].phys_beg)
                        phys_avail[i].phys_end = phys_avail[i].phys_beg;
        }

        /*
         * Locate largest block
         */
        for (i = 0; phys_avail[i].phys_end; ++i) {
                vm_paddr_t size = phys_avail[i].phys_end -
                                  phys_avail[i].phys_beg;

                if (size > biggestsize) {
                        biggestone = i;
                        biggestsize = size;
                }
                total += size;
        }
        --i;    /* adjust to last entry for use down below */

        end = phys_avail[biggestone].phys_end;
        end = trunc_page(end);

        /*
         * Initialize the queue headers for the free queue, the active queue
         * and the inactive queue.
         */
        vm_page_queue_init();

#if !defined(_KERNEL_VIRTUAL)
        /*
         * VKERNELs don't support minidumps and as such don't need
         * vm_page_dump
         *
         * Allocate a bitmap to indicate that a random physical page
         * needs to be included in a minidump.
         *
         * The amd64 port needs this to indicate which direct map pages
         * need to be dumped, via calls to dump_add_page()/dump_drop_page().
         *
         * However, i386 still needs this workspace internally within the
         * minidump code.  In theory, they are not needed on i386, but are
         * included should the sf_buf code decide to use them.
         */
        page_range = phys_avail[i].phys_end / PAGE_SIZE;
        vm_page_dump_size = round_page(roundup2(page_range, NBBY) / NBBY);
        end -= vm_page_dump_size;
        vm_page_dump = (void *)pmap_map(&vaddr, end, end + vm_page_dump_size,
                                        VM_PROT_READ | VM_PROT_WRITE);
        bzero((void *)vm_page_dump, vm_page_dump_size);
#endif
        /*
         * Compute the number of pages of memory that will be available for
         * use (taking into account the overhead of a page structure per
         * page).
         */
        first_page = phys_avail[0].phys_beg / PAGE_SIZE;
        page_range = phys_avail[i].phys_end / PAGE_SIZE - first_page;
        npages = (total - (page_range * sizeof(struct vm_page))) / PAGE_SIZE;

#ifndef _KERNEL_VIRTUAL
        /*
         * (only applies to real kernels)
         *
         * Reserve a large amount of low memory for potential 32-bit DMA
         * space allocations.  Once device initialization is complete we
         * release most of it, but keep (vm_dma_reserved) memory reserved
         * for later use.  Typically for X / graphics.  Through trial and
         * error we find that GPUs usually requires ~60-100MB or so.
         *
         * By default, 128M is left in reserve on machines with 2G+ of ram.
         */
        vm_low_phys_reserved = (vm_paddr_t)65536 << PAGE_SHIFT;
        if (vm_low_phys_reserved > total / 4)
                vm_low_phys_reserved = total / 4;
        if (vm_dma_reserved == 0) {
                vm_dma_reserved = 128 * 1024 * 1024;    /* 128MB */
                if (vm_dma_reserved > total / 16)
                        vm_dma_reserved = total / 16;
        }
#endif
        alist_init(&vm_contig_alist, 65536, vm_contig_ameta,
                   ALIST_RECORDS_65536);

        /*
         * Initialize the mem entry structures now, and put them in the free
         * queue.
         */
        new_end = trunc_page(end - page_range * sizeof(struct vm_page));
        mapped = pmap_map(&vaddr, new_end, end, VM_PROT_READ | VM_PROT_WRITE);
        vm_page_array = (vm_page_t)mapped;

#if defined(__x86_64__) && !defined(_KERNEL_VIRTUAL)
        /*
         * since pmap_map on amd64 returns stuff out of a direct-map region,
         * we have to manually add these pages to the minidump tracking so
         * that they can be dumped, including the vm_page_array.
         */
        for (pa = new_end;
             pa < phys_avail[biggestone].phys_end;
             pa += PAGE_SIZE) {
                dump_add_page(pa);
        }
#endif

        /*
         * Clear all of the page structures, run basic initialization so
         * PHYS_TO_VM_PAGE() operates properly even on pages not in the
         * map.
         */
        bzero((caddr_t) vm_page_array, page_range * sizeof(struct vm_page));
        vm_page_array_size = page_range;

        m = &vm_page_array[0];
        pa = ptoa(first_page);
        for (i = 0; i < page_range; ++i) {
                spin_init(&m->spin, "vm_page");
                m->phys_addr = pa;
                pa += PAGE_SIZE;
                ++m;
        }

        /*
         * Construct the free queue(s) in ascending order (by physical
         * address) so that the first 16MB of physical memory is allocated
         * last rather than first.  On large-memory machines, this avoids
         * the exhaustion of low physical memory before isa_dmainit has run.
         */
        vmstats.v_page_count = 0;
        vmstats.v_free_count = 0;
        for (i = 0; phys_avail[i].phys_end && npages > 0; ++i) {
                pa = phys_avail[i].phys_beg;
                if (i == biggestone)
                        last_pa = new_end;
                else
                        last_pa = phys_avail[i].phys_end;
                while (pa < last_pa && npages-- > 0) {
                        vm_add_new_page(pa);
                        pa += PAGE_SIZE;
                }
        }
        if (virtual2_start)
                virtual2_start = vaddr;
        else
                virtual_start = vaddr;
        mycpu->gd_vmstats = vmstats;
}

/*
 * Reorganize VM pages based on numa data.  May be called as many times as
 * necessary.  Will reorganize the vm_page_t page color and related queue(s)
 * to allow vm_page_alloc() to choose pages based on socket affinity.
 *
 * NOTE: This function is only called while we are still in UP mode, so
 *       we only need a critical section to protect the queues (which
 *       saves a lot of time, there are likely a ton of pages).
 */
void
vm_numa_organize(vm_paddr_t ran_beg, vm_paddr_t bytes, int physid)
{
        vm_paddr_t scan_beg;
        vm_paddr_t scan_end;
        vm_paddr_t ran_end;
        struct vpgqueues *vpq;
        vm_page_t m;
        vm_page_t mend;
        int i;
        int socket_mod;
        int socket_value;

        /*
         * Check if no physical information, or there was only one socket
         * (so don't waste time doing nothing!).
         */
        if (cpu_topology_phys_ids <= 1 ||
            cpu_topology_core_ids == 0) {
                return;
        }

        /*
         * Setup for our iteration.  Note that ACPI may iterate CPU
         * sockets starting at 0 or 1 or some other number.  The
         * cpu_topology code mod's it against the socket count.
         */
        ran_end = ran_beg + bytes;
        physid %= cpu_topology_phys_ids;

        socket_mod = PQ_L2_SIZE / cpu_topology_phys_ids;
        socket_value = physid * socket_mod;
        mend = &vm_page_array[vm_page_array_size];

        crit_enter();

        /*
         * Adjust vm_page->pc and requeue all affected pages.  The
         * allocator will then be able to localize memory allocations
         * to some degree.
         */
        for (i = 0; phys_avail[i].phys_end; ++i) {
                scan_beg = phys_avail[i].phys_beg;
                scan_end = phys_avail[i].phys_end;
                if (scan_end <= ran_beg)
                        continue;
                if (scan_beg >= ran_end)
                        continue;
                if (scan_beg < ran_beg)
                        scan_beg = ran_beg;
                if (scan_end > ran_end)
                        scan_end = ran_end;
                if (atop(scan_end) > first_page + vm_page_array_size)
                        scan_end = ptoa(first_page + vm_page_array_size);

                m = PHYS_TO_VM_PAGE(scan_beg);
                while (scan_beg < scan_end) {
                        KKASSERT(m < mend);
                        if (m->queue != PQ_NONE) {
                                vpq = &vm_page_queues[m->queue];
                                TAILQ_REMOVE(&vpq->pl, m, pageq);
                                --vpq->lcnt;
                                /* queue doesn't change, no need to adj cnt */
                                m->queue -= m->pc;
                                m->pc %= socket_mod;
                                m->pc += socket_value;
                                m->pc &= PQ_L2_MASK;
                                m->queue += m->pc;
                                vpq = &vm_page_queues[m->queue];
                                TAILQ_INSERT_HEAD(&vpq->pl, m, pageq);
                                ++vpq->lcnt;
                                /* queue doesn't change, no need to adj cnt */
                        } else {
                                m->pc %= socket_mod;
                                m->pc += socket_value;
                                m->pc &= PQ_L2_MASK;
                        }
                        scan_beg += PAGE_SIZE;
                        ++m;
                }
        }
        crit_exit();
}

/*
 * We tended to reserve a ton of memory for contigmalloc().  Now that most
 * drivers have initialized we want to return most the remaining free
 * reserve back to the VM page queues so they can be used for normal
 * allocations.
 *
 * We leave vm_dma_reserved bytes worth of free pages in the reserve pool.
 *
 * Also setup the action_hash[] table here (which is only used by userland)
 */
static void
vm_page_startup_finish(void *dummy __unused)
{
        alist_blk_t blk;
        alist_blk_t rblk;
        alist_blk_t count;
        alist_blk_t xcount;
        alist_blk_t bfree;
        vm_page_t m;
        int i;

        spin_lock(&vm_contig_spin);
        for (;;) {
                bfree = alist_free_info(&vm_contig_alist, &blk, &count);
                if (bfree <= vm_dma_reserved / PAGE_SIZE)
                        break;
                if (count == 0)
                        break;

                /*
                 * Figure out how much of the initial reserve we have to
                 * free in order to reach our target.
                 */
                bfree -= vm_dma_reserved / PAGE_SIZE;
                if (count > bfree) {
                        blk += count - bfree;
                        count = bfree;
                }

                /*
                 * Calculate the nearest power of 2 <= count.
                 */
                for (xcount = 1; xcount <= count; xcount <<= 1)
                        ;
                xcount >>= 1;
                blk += count - xcount;
                count = xcount;

                /*
                 * Allocate the pages from the alist, then free them to
                 * the normal VM page queues.
                 *
                 * Pages allocated from the alist are wired.  We have to
                 * busy, unwire, and free them.  We must also adjust
                 * vm_low_phys_reserved before freeing any pages to prevent
                 * confusion.
                 */
                rblk = alist_alloc(&vm_contig_alist, blk, count);
                if (rblk != blk) {
                        kprintf("vm_page_startup_finish: Unable to return "
                                "dma space @0x%08x/%d -> 0x%08x\n",
                                blk, count, rblk);
                        break;
                }
                atomic_add_int(&vmstats.v_dma_pages, -count);
                spin_unlock(&vm_contig_spin);

                m = PHYS_TO_VM_PAGE((vm_paddr_t)blk << PAGE_SHIFT);
                vm_low_phys_reserved = VM_PAGE_TO_PHYS(m);
                while (count) {
                        vm_page_busy_wait(m, FALSE, "cpgfr");
                        vm_page_unwire(m, 0);
                        vm_page_free(m);
                        --count;
                        ++m;
                }
                spin_lock(&vm_contig_spin);
        }
        spin_unlock(&vm_contig_spin);

        /*
         * Print out how much DMA space drivers have already allocated and
         * how much is left over.
         */
        kprintf("DMA space used: %jdk, remaining available: %jdk\n",
                (intmax_t)(vmstats.v_dma_pages - vm_contig_alist.bl_free) *
                (PAGE_SIZE / 1024),
                (intmax_t)vm_contig_alist.bl_free * (PAGE_SIZE / 1024));

        /*
         * Scale the action_hash[] array.  Primary contention occurs due
         * to cpu locks, scaled to ncpus, and scan overhead may be incurred
         * depending on the number of threads, which we scale to maxproc.
         *
         * NOTE: Action lock might recurse due to callback, so allow
         *       recursion.
         */
        vmaction_hsize = VMACTION_MINHSIZE;
        if (vmaction_hsize < ncpus * 2)
                vmaction_hsize = ncpus * 2;
        if (vmaction_hsize < maxproc / 16)
                vmaction_hsize = maxproc / 16;
        vmaction_hmask = 1;
        while (vmaction_hmask < vmaction_hsize)
                vmaction_hmask = (vmaction_hmask << 1) | 1;
        vmaction_hsize = vmaction_hmask + 1;

        action_hash = kmalloc(sizeof(action_hash[0]) * vmaction_hsize,
                              M_ACTIONHASH,
                              M_WAITOK | M_ZERO);

        for (i = 0; i < vmaction_hsize; i++) {
                LIST_INIT(&action_hash[i].list);
                lockinit(&action_hash[i].lk, "actlk", 0, LK_CANRECURSE);
        }
}
SYSINIT(vm_pgend, SI_SUB_PROC0_POST, SI_ORDER_ANY,
        vm_page_startup_finish, NULL);


/*
 * Scan comparison function for Red-Black tree scans.  An inclusive
 * (start,end) is expected.  Other fields are not used.
 */
int
rb_vm_page_scancmp(struct vm_page *p, void *data)
{
        struct rb_vm_page_scan_info *info = data;

        if (p->pindex < info->start_pindex)
                return(-1);
        if (p->pindex > info->end_pindex)
                return(1);
        return(0);
}

int
rb_vm_page_compare(struct vm_page *p1, struct vm_page *p2)
{
        if (p1->pindex < p2->pindex)
                return(-1);
        if (p1->pindex > p2->pindex)
                return(1);
        return(0);
}

void
vm_page_init(vm_page_t m)
{
        /* do nothing for now.  Called from pmap_page_init() */
}

/*
 * Each page queue has its own spin lock, which is fairly optimal for
 * allocating and freeing pages at least.
 *
 * The caller must hold the vm_page_spin_lock() before locking a vm_page's
 * queue spinlock via this function.  Also note that m->queue cannot change
 * unless both the page and queue are locked.
 */
static __inline
void
_vm_page_queue_spin_lock(vm_page_t m)
{
        u_short queue;

        queue = m->queue;
        if (queue != PQ_NONE) {
                spin_lock(&vm_page_queues[queue].spin);
                KKASSERT(queue == m->queue);
        }
}

static __inline
void
_vm_page_queue_spin_unlock(vm_page_t m)
{
        u_short queue;

        queue = m->queue;
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_unlock(&vm_page_queues[queue].spin);
}

static __inline
void
_vm_page_queues_spin_lock(u_short queue)
{
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_lock(&vm_page_queues[queue].spin);
}


static __inline
void
_vm_page_queues_spin_unlock(u_short queue)
{
        cpu_ccfence();
        if (queue != PQ_NONE)
                spin_unlock(&vm_page_queues[queue].spin);
}

void
vm_page_queue_spin_lock(vm_page_t m)
{
        _vm_page_queue_spin_lock(m);
}

void
vm_page_queues_spin_lock(u_short queue)
{
        _vm_page_queues_spin_lock(queue);
}

void
vm_page_queue_spin_unlock(vm_page_t m)
{
        _vm_page_queue_spin_unlock(m);
}

void
vm_page_queues_spin_unlock(u_short queue)
{
        _vm_page_queues_spin_unlock(queue);
}

/*
 * This locks the specified vm_page and its queue in the proper order
 * (page first, then queue).  The queue may change so the caller must
 * recheck on return.
 */
static __inline
void
_vm_page_and_queue_spin_lock(vm_page_t m)
{
        vm_page_spin_lock(m);
        _vm_page_queue_spin_lock(m);
}

static __inline
void
_vm_page_and_queue_spin_unlock(vm_page_t m)
{
        _vm_page_queues_spin_unlock(m->queue);
        vm_page_spin_unlock(m);
}

void
vm_page_and_queue_spin_unlock(vm_page_t m)
{
        _vm_page_and_queue_spin_unlock(m);
}

void
vm_page_and_queue_spin_lock(vm_page_t m)
{
        _vm_page_and_queue_spin_lock(m);
}

/*
 * Helper function removes vm_page from its current queue.
 * Returns the base queue the page used to be on.
 *
 * The vm_page and the queue must be spinlocked.
 * This function will unlock the queue but leave the page spinlocked.
 */
static __inline u_short
_vm_page_rem_queue_spinlocked(vm_page_t m)
{
        struct vpgqueues *pq;
        u_short queue;
        u_short oqueue;
        int *cnt;

        queue = m->queue;
        if (queue != PQ_NONE) {
                pq = &vm_page_queues[queue];
                TAILQ_REMOVE(&pq->pl, m, pageq);

                /*
                 * Adjust our pcpu stats.  In order for the nominal low-memory
                 * algorithms to work properly we don't let any pcpu stat get
                 * too negative before we force it to be rolled-up into the
                 * global stats.  Otherwise our pageout and vm_wait tests
                 * will fail badly.
                 *
                 * The idea here is to reduce unnecessary SMP cache
                 * mastership changes in the global vmstats, which can be
                 * particularly bad in multi-socket systems.
                 */
                cnt = (int *)((char *)&mycpu->gd_vmstats_adj + pq->cnt_offset);
                atomic_add_int(cnt, -1);
                if (*cnt < -VMMETER_SLOP_COUNT) {
                        u_int copy = atomic_swap_int(cnt, 0);
                        cnt = (int *)((char *)&vmstats + pq->cnt_offset);
                        atomic_add_int(cnt, copy);
                        cnt = (int *)((char *)&mycpu->gd_vmstats +
                                      pq->cnt_offset);
                        atomic_add_int(cnt, copy);
                }
                pq->lcnt--;
                m->queue = PQ_NONE;
                oqueue = queue;
                queue -= m->pc;
                vm_page_queues_spin_unlock(oqueue);     /* intended */
        }
        return queue;
}

/*
 * Helper function places the vm_page on the specified queue.  Generally
 * speaking only PQ_FREE pages are placed at the head, to allow them to
 * be allocated sooner rather than later on the assumption that they
 * are cache-hot.
 *
 * The vm_page must be spinlocked.
 * This function will return with both the page and the queue locked.
 */
static __inline void
_vm_page_add_queue_spinlocked(vm_page_t m, u_short queue, int athead)
{
        struct vpgqueues *pq;
        u_int *cnt;

        KKASSERT(m->queue == PQ_NONE);

        if (queue != PQ_NONE) {
                vm_page_queues_spin_lock(queue);
                pq = &vm_page_queues[queue];
                ++pq->lcnt;

                /*
                 * Adjust our pcpu stats.  If a system entity really needs
                 * to incorporate the count it will call vmstats_rollup()
                 * to roll it all up into the global vmstats strufture.
                 */
                cnt = (int *)((char *)&mycpu->gd_vmstats_adj + pq->cnt_offset);
                atomic_add_int(cnt, 1);

                /*
                 * PQ_FREE is always handled LIFO style to try to provide
                 * cache-hot pages to programs.
                 */
                m->queue = queue;
                if (queue - m->pc == PQ_FREE) {
                        TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
                } else if (athead) {
                        TAILQ_INSERT_HEAD(&pq->pl, m, pageq);
                } else {
                        TAILQ_INSERT_TAIL(&pq->pl, m, pageq);
                }
                /* leave the queue spinlocked */
        }
}

/*
 * Wait until page is no longer PG_BUSY or (if also_m_busy is TRUE)
 * m->busy is zero.  Returns TRUE if it had to sleep, FALSE if we
 * did not.  Only one sleep call will be made before returning.
 *
 * This function does NOT busy the page and on return the page is not
 * guaranteed to be available.
 */
void
vm_page_sleep_busy(vm_page_t m, int also_m_busy, const char *msg)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();

                if ((flags & PG_BUSY) == 0 &&
                    (also_m_busy == 0 || (flags & PG_SBUSY) == 0)) {
                        break;
                }
                tsleep_interlock(m, 0);
                if (atomic_cmpset_int(&m->flags, flags,
                                      flags | PG_WANTED | PG_REFERENCED)) {
                        tsleep(m, PINTERLOCKED, msg, 0);
                        break;
                }
        }
}

/*
 * This calculates and returns a page color given an optional VM object and
 * either a pindex or an iterator.  We attempt to return a cpu-localized
 * pg_color that is still roughly 16-way set-associative.  The CPU topology
 * is used if it was probed.
 *
 * The caller may use the returned value to index into e.g. PQ_FREE when
 * allocating a page in order to nominally obtain pages that are hopefully
 * already localized to the requesting cpu.  This function is not able to
 * provide any sort of guarantee of this, but does its best to improve
 * hardware cache management performance.
 *
 * WARNING! The caller must mask the returned value with PQ_L2_MASK.
 */
u_short
vm_get_pg_color(int cpuid, vm_object_t object, vm_pindex_t pindex)
{
        u_short pg_color;
        int phys_id;
        int core_id;
        int object_pg_color;

        phys_id = get_cpu_phys_id(cpuid);
        core_id = get_cpu_core_id(cpuid);
        object_pg_color = object ? object->pg_color : 0;

        if (cpu_topology_phys_ids && cpu_topology_core_ids) {
                int grpsize;

                /*
                 * Break us down by socket and cpu
                 */
                pg_color = phys_id * PQ_L2_SIZE / cpu_topology_phys_ids;
                pg_color += core_id * PQ_L2_SIZE /
                            (cpu_topology_core_ids * cpu_topology_phys_ids);

                /*
                 * Calculate remaining component for object/queue color
                 */
                grpsize = PQ_L2_SIZE / (cpu_topology_core_ids *
                                        cpu_topology_phys_ids);
                if (grpsize >= 8) {
                        pg_color += (pindex + object_pg_color) % grpsize;
                } else {
                        if (grpsize <= 2) {
                                grpsize = 8;
                        } else {
                                /* 3->9, 4->8, 5->10, 6->12, 7->14 */
                                grpsize += grpsize;
                                if (grpsize < 8)
                                        grpsize += grpsize;
                        }
                        pg_color += (pindex + object_pg_color) % grpsize;
                }
        } else {
                /*
                 * Unknown topology, distribute things evenly.
                 */
                pg_color = cpuid * PQ_L2_SIZE / ncpus;
                pg_color += pindex + object_pg_color;
        }
        return (pg_color & PQ_L2_MASK);
}

/*
 * Wait until PG_BUSY can be set, then set it.  If also_m_busy is TRUE we
 * also wait for m->busy to become 0 before setting PG_BUSY.
 */
void
VM_PAGE_DEBUG_EXT(vm_page_busy_wait)(vm_page_t m,
                                     int also_m_busy, const char *msg
                                     VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                        }
                } else if (also_m_busy && (flags & PG_SBUSY)) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                        }
                } else {
                        if (atomic_cmpset_int(&m->flags, flags,
                                              flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                                m->busy_func = func;
                                m->busy_line = lineno;
#endif
                                break;
                        }
                }
        }
}

/*
 * Attempt to set PG_BUSY.  If also_m_busy is TRUE we only succeed if m->busy
 * is also 0.
 *
 * Returns non-zero on failure.
 */
int
VM_PAGE_DEBUG_EXT(vm_page_busy_try)(vm_page_t m, int also_m_busy
                                    VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY)
                        return TRUE;
                if (also_m_busy && (flags & PG_SBUSY))
                        return TRUE;
                if (atomic_cmpset_int(&m->flags, flags, flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                                m->busy_func = func;
                                m->busy_line = lineno;
#endif
                        return FALSE;
                }
        }
}

/*
 * Clear the PG_BUSY flag and return non-zero to indicate to the caller
 * that a wakeup() should be performed.
 *
 * The vm_page must be spinlocked and will remain spinlocked on return.
 * The related queue must NOT be spinlocked (which could deadlock us).
 *
 * (inline version)
 */
static __inline
int
_vm_page_wakeup(vm_page_t m)
{
        u_int32_t flags;

        for (;;) {
                flags = m->flags;
                cpu_ccfence();
                if (atomic_cmpset_int(&m->flags, flags,
                                      flags & ~(PG_BUSY | PG_WANTED))) {
                        break;
                }
        }
        return(flags & PG_WANTED);
}

/*
 * Clear the PG_BUSY flag and wakeup anyone waiting for the page.  This
 * is typically the last call you make on a page before moving onto
 * other things.
 */
void
vm_page_wakeup(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
        vm_page_spin_lock(m);
        if (_vm_page_wakeup(m)) {
                vm_page_spin_unlock(m);
                wakeup(m);
        } else {
                vm_page_spin_unlock(m);
        }
}

/*
 * Holding a page keeps it from being reused.  Other parts of the system
 * can still disassociate the page from its current object and free it, or
 * perform read or write I/O on it and/or otherwise manipulate the page,
 * but if the page is held the VM system will leave the page and its data
 * intact and not reuse the page for other purposes until the last hold
 * reference is released.  (see vm_page_wire() if you want to prevent the
 * page from being disassociated from its object too).
 *
 * The caller must still validate the contents of the page and, if necessary,
 * wait for any pending I/O (e.g. vm_page_sleep_busy() loop) to complete
 * before manipulating the page.
 *
 * XXX get vm_page_spin_lock() here and move FREE->HOLD if necessary
 */
void
vm_page_hold(vm_page_t m)
{
        vm_page_spin_lock(m);
        atomic_add_int(&m->hold_count, 1);
        if (m->queue - m->pc == PQ_FREE) {
                _vm_page_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_HOLD + m->pc, 0);
                _vm_page_queue_spin_unlock(m);
        }
        vm_page_spin_unlock(m);
}

/*
 * The opposite of vm_page_hold().  If the page is on the HOLD queue
 * it was freed while held and must be moved back to the FREE queue.
 */
void
vm_page_unhold(vm_page_t m)
{
        KASSERT(m->hold_count > 0 && m->queue - m->pc != PQ_FREE,
                ("vm_page_unhold: pg %p illegal hold_count (%d) or on FREE queue (%d)",
                 m, m->hold_count, m->queue - m->pc));
        vm_page_spin_lock(m);
        atomic_add_int(&m->hold_count, -1);
        if (m->hold_count == 0 && m->queue - m->pc == PQ_HOLD) {
                _vm_page_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_FREE + m->pc, 1);
                _vm_page_queue_spin_unlock(m);
        }
        vm_page_spin_unlock(m);
}

/*
 *      vm_page_getfake:
 *
 *      Create a fictitious page with the specified physical address and
 *      memory attribute.  The memory attribute is the only the machine-
 *      dependent aspect of a fictitious page that must be initialized.
 */

void
vm_page_initfake(vm_page_t m, vm_paddr_t paddr, vm_memattr_t memattr)
{

        if ((m->flags & PG_FICTITIOUS) != 0) {
                /*
                 * The page's memattr might have changed since the
                 * previous initialization.  Update the pmap to the
                 * new memattr.
                 */
                goto memattr;
        }
        m->phys_addr = paddr;
        m->queue = PQ_NONE;
        /* Fictitious pages don't use "segind". */
        /* Fictitious pages don't use "order" or "pool". */
        m->flags = PG_FICTITIOUS | PG_UNMANAGED | PG_BUSY;
        m->wire_count = 1;
        spin_init(&m->spin, "fake_page");
        pmap_page_init(m);
memattr:
        pmap_page_set_memattr(m, memattr);
}

/*
 * Inserts the given vm_page into the object and object list.
 *
 * The pagetables are not updated but will presumably fault the page
 * in if necessary, or if a kernel page the caller will at some point
 * enter the page into the kernel's pmap.  We are not allowed to block
 * here so we *can't* do this anyway.
 *
 * This routine may not block.
 * This routine must be called with the vm_object held.
 * This routine must be called with a critical section held.
 *
 * This routine returns TRUE if the page was inserted into the object
 * successfully, and FALSE if the page already exists in the object.
 */
int
vm_page_insert(vm_page_t m, vm_object_t object, vm_pindex_t pindex)
{
        ASSERT_LWKT_TOKEN_HELD_EXCL(vm_object_token(object));
        if (m->object != NULL)
                panic("vm_page_insert: already inserted");

        atomic_add_int(&object->generation, 1);

        /*
         * Record the object/offset pair in this page and add the
         * pv_list_count of the page to the object.
         *
         * The vm_page spin lock is required for interactions with the pmap.
         */
        vm_page_spin_lock(m);
        m->object = object;
        m->pindex = pindex;
        if (vm_page_rb_tree_RB_INSERT(&object->rb_memq, m)) {
                m->object = NULL;
                m->pindex = 0;
                vm_page_spin_unlock(m);
                return FALSE;
        }
        ++object->resident_page_count;
        ++mycpu->gd_vmtotal.t_rm;
        vm_page_spin_unlock(m);

        /*
         * Since we are inserting a new and possibly dirty page,
         * update the object's OBJ_WRITEABLE and OBJ_MIGHTBEDIRTY flags.
         */
        if ((m->valid & m->dirty) ||
            (m->flags & (PG_WRITEABLE | PG_NEED_COMMIT)))
                vm_object_set_writeable_dirty(object);

        /*
         * Checks for a swap assignment and sets PG_SWAPPED if appropriate.
         */
        swap_pager_page_inserted(m);
        return TRUE;
}

/*
 * Removes the given vm_page_t from the (object,index) table
 *
 * The underlying pmap entry (if any) is NOT removed here.
 * This routine may not block.
 *
 * The page must be BUSY and will remain BUSY on return.
 * No other requirements.
 *
 * NOTE: FreeBSD side effect was to unbusy the page on return.  We leave
 *       it busy.
 */
void
vm_page_remove(vm_page_t m)
{
        vm_object_t object;

        if (m->object == NULL) {
                return;
        }

        if ((m->flags & PG_BUSY) == 0)
                panic("vm_page_remove: page not busy");

        object = m->object;

        vm_object_hold(object);

        /*
         * Remove the page from the object and update the object.
         *
         * The vm_page spin lock is required for interactions with the pmap.
         */
        vm_page_spin_lock(m);
        vm_page_rb_tree_RB_REMOVE(&object->rb_memq, m);
        --object->resident_page_count;
        --mycpu->gd_vmtotal.t_rm;
        m->object = NULL;
        atomic_add_int(&object->generation, 1);
        vm_page_spin_unlock(m);

        vm_object_drop(object);
}

/*
 * Locate and return the page at (object, pindex), or NULL if the
 * page could not be found.
 *
 * The caller must hold the vm_object token.
 */
vm_page_t
vm_page_lookup(vm_object_t object, vm_pindex_t pindex)
{
        vm_page_t m;

        /*
         * Search the hash table for this object/offset pair
         */
        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        KKASSERT(m == NULL || (m->object == object && m->pindex == pindex));
        return(m);
}

vm_page_t
VM_PAGE_DEBUG_EXT(vm_page_lookup_busy_wait)(struct vm_object *object,
                                            vm_pindex_t pindex,
                                            int also_m_busy, const char *msg
                                            VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;
        vm_page_t m;

        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        while (m) {
                KKASSERT(m->object == object && m->pindex == pindex);
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                                m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq,
                                                              pindex);
                        }
                } else if (also_m_busy && (flags & PG_SBUSY)) {
                        tsleep_interlock(m, 0);
                        if (atomic_cmpset_int(&m->flags, flags,
                                          flags | PG_WANTED | PG_REFERENCED)) {
                                tsleep(m, PINTERLOCKED, msg, 0);
                                m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq,
                                                              pindex);
                        }
                } else if (atomic_cmpset_int(&m->flags, flags,
                                             flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                        m->busy_func = func;
                        m->busy_line = lineno;
#endif
                        break;
                }
        }
        return m;
}

/*
 * Attempt to lookup and busy a page.
 *
 * Returns NULL if the page could not be found
 *
 * Returns a vm_page and error == TRUE if the page exists but could not
 * be busied.
 *
 * Returns a vm_page and error == FALSE on success.
 */
vm_page_t
VM_PAGE_DEBUG_EXT(vm_page_lookup_busy_try)(struct vm_object *object,
                                           vm_pindex_t pindex,
                                           int also_m_busy, int *errorp
                                           VM_PAGE_DEBUG_ARGS)
{
        u_int32_t flags;
        vm_page_t m;

        ASSERT_LWKT_TOKEN_HELD(vm_object_token(object));
        m = vm_page_rb_tree_RB_LOOKUP(&object->rb_memq, pindex);
        *errorp = FALSE;
        while (m) {
                KKASSERT(m->object == object && m->pindex == pindex);
                flags = m->flags;
                cpu_ccfence();
                if (flags & PG_BUSY) {
                        *errorp = TRUE;
                        break;
                }
                if (also_m_busy && (flags & PG_SBUSY)) {
                        *errorp = TRUE;
                        break;
                }
                if (atomic_cmpset_int(&m->flags, flags, flags | PG_BUSY)) {
#ifdef VM_PAGE_DEBUG
                        m->busy_func = func;
                        m->busy_line = lineno;
#endif
                        break;
                }
        }
        return m;
}

/*
 * Attempt to repurpose the passed-in page.  If the passed-in page cannot
 * be repurposed it will be released, *must_reenter will be set to 1, and
 * this function will fall-through to vm_page_lookup_busy_try().
 *
 * The passed-in page must be wired and not busy.  The returned page will
 * be busied and not wired.
 *
 * A different page may be returned.  The returned page will be busied and
 * not wired.
 *
 * NULL can be returned.  If so, the required page could not be busied.
 * The passed-in page will be unwired.
 */
vm_page_t
vm_page_repurpose(struct vm_object *object, vm_pindex_t pindex,
                  int also_m_busy, int *errorp, vm_page_t m,
                  int *must_reenter, int *iswired)
{
        if (m) {
                /*
                 * Do not mess with pages in a complex state, such as pages
                 * which are mapped, as repurposing such pages can be more
                 * expensive than simply allocatin a new one.
                 *
                 * NOTE: Soft-busying can deadlock against putpages or I/O
                 *       so we only allow hard-busying here.
                 */
                KKASSERT(also_m_busy == FALSE);
                vm_page_busy_wait(m, also_m_busy, "biodep");

                if ((m->flags & (PG_UNMANAGED | PG_MAPPED |
                                 PG_FICTITIOUS | PG_SBUSY)) ||
                    m->busy || m->wire_count != 1 || m->hold_count) {
                        vm_page_unwire(m, 0);
                        vm_page_wakeup(m);
                        /* fall through to normal lookup */
                } else if (m->dirty || (m->flags & PG_NEED_COMMIT)) {
                        vm_page_unwire(m, 0);
                        vm_page_deactivate(m);
                        vm_page_wakeup(m);
                        /* fall through to normal lookup */
                } else {
                        /*
                         * We can safely repurpose the page.  It should
                         * already be unqueued.
                         */
                        KKASSERT(m->queue == PQ_NONE && m->dirty == 0);
                        vm_page_remove(m);
                        m->valid = 0;
                        m->act_count = 0;
                        if (vm_page_insert(m, object, pindex)) {
                                *errorp = 0;
                                *iswired = 1;

                                return m;
                        }
                        vm_page_unwire(m, 0);
                        vm_page_free(m);
                        /* fall through to normal lookup */
                }
        }

        /*
         * Cannot repurpose page, attempt to locate the desired page.  May
         * return NULL.
         */
        *must_reenter = 1;
        *iswired = 0;
        m = vm_page_lookup_busy_try(object, pindex, also_m_busy, errorp);

        return m;
}

/*
 * Caller must hold the related vm_object
 */
vm_page_t
vm_page_next(vm_page_t m)
{
        vm_page_t next;

        next = vm_page_rb_tree_RB_NEXT(m);
        if (next && next->pindex != m->pindex + 1)
                next = NULL;
        return (next);
}

/*
 * vm_page_rename()
 *
 * Move the given vm_page from its current object to the specified
 * target object/offset.  The page must be busy and will remain so
 * on return.
 *
 * new_object must be held.
 * This routine might block. XXX ?
 *
 * NOTE: Swap associated with the page must be invalidated by the move.  We
 *       have to do this for several reasons:  (1) we aren't freeing the
 *       page, (2) we are dirtying the page, (3) the VM system is probably
 *       moving the page from object A to B, and will then later move
 *       the backing store from A to B and we can't have a conflict.
 *
 * NOTE: We *always* dirty the page.  It is necessary both for the
 *       fact that we moved it, and because we may be invalidating
 *       swap.  If the page is on the cache, we have to deactivate it
 *       or vm_page_dirty() will panic.  Dirty pages are not allowed
 *       on the cache.
 */
void
vm_page_rename(vm_page_t m, vm_object_t new_object, vm_pindex_t new_pindex)
{
        KKASSERT(m->flags & PG_BUSY);
        ASSERT_LWKT_TOKEN_HELD_EXCL(vm_object_token(new_object));
        if (m->object) {
                ASSERT_LWKT_TOKEN_HELD_EXCL(vm_object_token(m->object));
                vm_page_remove(m);
        }
        if (vm_page_insert(m, new_object, new_pindex) == FALSE) {
                panic("vm_page_rename: target exists (%p,%"PRIu64")",
                      new_object, new_pindex);
        }
        if (m->queue - m->pc == PQ_CACHE)
                vm_page_deactivate(m);
        vm_page_dirty(m);
}

/*
 * vm_page_unqueue() without any wakeup.  This routine is used when a page
 * is to remain BUSYied by the caller.
 *
 * This routine may not block.
 */
void
vm_page_unqueue_nowakeup(vm_page_t m)
{
        vm_page_and_queue_spin_lock(m);
        (void)_vm_page_rem_queue_spinlocked(m);
        vm_page_spin_unlock(m);
}

/*
 * vm_page_unqueue() - Remove a page from its queue, wakeup the pagedemon
 * if necessary.
 *
 * This routine may not block.
 */
void
vm_page_unqueue(vm_page_t m)
{
        u_short queue;

        vm_page_and_queue_spin_lock(m);
        queue = _vm_page_rem_queue_spinlocked(m);
        if (queue == PQ_FREE || queue == PQ_CACHE) {
                vm_page_spin_unlock(m);
                pagedaemon_wakeup();
        } else {
                vm_page_spin_unlock(m);
        }
}

/*
 * vm_page_list_find()
 *
 * Find a page on the specified queue with color optimization.
 *
 * The page coloring optimization attempts to locate a page that does
 * not overload other nearby pages in the object in the cpu's L1 or L2
 * caches.  We need this optimization because cpu caches tend to be
 * physical caches, while object spaces tend to be virtual.
 *
 * The page coloring optimization also, very importantly, tries to localize
 * memory to cpus and physical sockets.
 *
 * On MP systems each PQ_FREE and PQ_CACHE color queue has its own spinlock
 * and the algorithm is adjusted to localize allocations on a per-core basis.
 * This is done by 'twisting' the colors.
 *
 * The page is returned spinlocked and removed from its queue (it will
 * be on PQ_NONE), or NULL. The page is not PG_BUSY'd.  The caller
 * is responsible for dealing with the busy-page case (usually by
 * deactivating the page and looping).
 *
 * NOTE:  This routine is carefully inlined.  A non-inlined version
 *        is available for outside callers but the only critical path is
 *        from within this source file.
 *
 * NOTE:  This routine assumes that the vm_pages found in PQ_CACHE and PQ_FREE
 *        represent stable storage, allowing us to order our locks vm_page
 *        first, then queue.
 */
static __inline
vm_page_t
_vm_page_list_find(int basequeue, int index)
{
        vm_page_t m;

        for (;;) {
                m = TAILQ_FIRST(&vm_page_queues[basequeue+index].pl);
                if (m == NULL) {
                        m = _vm_page_list_find2(basequeue, index);
                        return(m);
                }
                vm_page_and_queue_spin_lock(m);
                if (m->queue == basequeue + index) {
                        _vm_page_rem_queue_spinlocked(m);
                        /* vm_page_t spin held, no queue spin */
                        break;
                }
                vm_page_and_queue_spin_unlock(m);
        }
        return(m);
}

/*
 * If we could not find the page in the desired queue try to find it in
 * a nearby queue.
 */
static vm_page_t
_vm_page_list_find2(int basequeue, int index)
{
        struct vpgqueues *pq;
        vm_page_t m = NULL;
        int pqmask = PQ_SET_ASSOC_MASK >> 1;
        int pqi;
        int i;

        index &= PQ_L2_MASK;
        pq = &vm_page_queues[basequeue];

        /*
         * Run local sets of 16, 32, 64, 128, and the whole queue if all
         * else fails (PQ_L2_MASK which is 255).
         */
        do {
                pqmask = (pqmask << 1) | 1;
                for (i = 0; i <= pqmask; ++i) {
                        pqi = (index & ~pqmask) | ((index + i) & pqmask);
                        m = TAILQ_FIRST(&pq[pqi].pl);
                        if (m) {
                                _vm_page_and_queue_spin_lock(m);
                                if (m->queue == basequeue + pqi) {
                                        _vm_page_rem_queue_spinlocked(m);
                                        return(m);
                                }
                                _vm_page_and_queue_spin_unlock(m);
                                --i;
                                continue;
                        }
                }
        } while (pqmask != PQ_L2_MASK);

        return(m);
}

/*
 * Returns a vm_page candidate for allocation.  The page is not busied so
 * it can move around.  The caller must busy the page (and typically
 * deactivate it if it cannot be busied!)
 *
 * Returns a spinlocked vm_page that has been removed from its queue.
 */
vm_page_t
vm_page_list_find(int basequeue, int index)
{
        return(_vm_page_list_find(basequeue, index));
}

/*
 * Find a page on the cache queue with color optimization, remove it
 * from the queue, and busy it.  The returned page will not be spinlocked.
 *
 * A candidate failure will be deactivated.  Candidates can fail due to
 * being busied by someone else, in which case they will be deactivated.
 *
 * This routine may not block.
 *
 */
static vm_page_t
vm_page_select_cache(u_short pg_color)
{
        vm_page_t m;

        for (;;) {
                m = _vm_page_list_find(PQ_CACHE, pg_color & PQ_L2_MASK);
                if (m == NULL)
                        break;
                /*
                 * (m) has been removed from its queue and spinlocked
                 */
                if (vm_page_busy_try(m, TRUE)) {
                        _vm_page_deactivate_locked(m, 0);
                        vm_page_spin_unlock(m);
                } else {
                        /*
                         * We successfully busied the page
                         */
                        if ((m->flags & (PG_UNMANAGED | PG_NEED_COMMIT)) == 0 &&
                            m->hold_count == 0 &&
                            m->wire_count == 0 &&
                            (m->dirty & m->valid) == 0) {
                                vm_page_spin_unlock(m);
                                pagedaemon_wakeup();
                                return(m);
                        }

                        /*
                         * The page cannot be recycled, deactivate it.
                         */
                        _vm_page_deactivate_locked(m, 0);
                        if (_vm_page_wakeup(m)) {
                                vm_page_spin_unlock(m);
                                wakeup(m);
                        } else {
                                vm_page_spin_unlock(m);
                        }
                }
        }
        return (m);
}

/*
 * Find a free page.  We attempt to inline the nominal case and fall back
 * to _vm_page_select_free() otherwise.  A busied page is removed from
 * the queue and returned.
 *
 * This routine may not block.
 */
static __inline vm_page_t
vm_page_select_free(u_short pg_color)
{
        vm_page_t m;

        for (;;) {
                m = _vm_page_list_find(PQ_FREE, pg_color & PQ_L2_MASK);
                if (m == NULL)
                        break;
                if (vm_page_busy_try(m, TRUE)) {
                        /*
                         * Various mechanisms such as a pmap_collect can
                         * result in a busy page on the free queue.  We
                         * have to move the page out of the way so we can
                         * retry the allocation.  If the other thread is not
                         * allocating the page then m->valid will remain 0 and
                         * the pageout daemon will free the page later on.
                         *
                         * Since we could not busy the page, however, we
                         * cannot make assumptions as to whether the page
                         * will be allocated by the other thread or not,
                         * so all we can do is deactivate it to move it out
                         * of the way.  In particular, if the other thread
                         * wires the page it may wind up on the inactive
                         * queue and the pageout daemon will have to deal
                         * with that case too.
                         */
                        _vm_page_deactivate_locked(m, 0);
                        vm_page_spin_unlock(m);
                } else {
                        /*
                         * Theoretically if we are able to busy the page
                         * atomic with the queue removal (using the vm_page
                         * lock) nobody else should be able to mess with the
                         * page before us.
                         */
                        KKASSERT((m->flags & (PG_UNMANAGED |
                                              PG_NEED_COMMIT)) == 0);
                        KASSERT(m->hold_count == 0, ("m->hold_count is not zero "
                                                     "pg %p q=%d flags=%08x hold=%d wire=%d",
                                                     m, m->queue, m->flags, m->hold_count, m->wire_count));
                        KKASSERT(m->wire_count == 0);
                        vm_page_spin_unlock(m);
                        pagedaemon_wakeup();

                        /* return busied and removed page */
                        return(m);
                }
        }
        return(m);
}

/*
 * vm_page_alloc()
 *
 * Allocate and return a memory cell associated with this VM object/offset
 * pair.  If object is NULL an unassociated page will be allocated.
 *
 * The returned page will be busied and removed from its queues.  This
 * routine can block and may return NULL if a race occurs and the page
 * is found to already exist at the specified (object, pindex).
 *
 *      VM_ALLOC_NORMAL         allow use of cache pages, nominal free drain
 *      VM_ALLOC_QUICK          like normal but cannot use cache
 *      VM_ALLOC_SYSTEM         greater free drain
 *      VM_ALLOC_INTERRUPT      allow free list to be completely drained
 *      VM_ALLOC_ZERO           advisory request for pre-zero'd page only
 *      VM_ALLOC_FORCE_ZERO     advisory request for pre-zero'd page only
 *      VM_ALLOC_NULL_OK        ok to return NULL on insertion collision
 *                              (see vm_page_grab())
 *      VM_ALLOC_USE_GD         ok to use per-gd cache
 *
 *      VM_ALLOC_CPU(n)         allocate using specified cpu localization
 *
 * The object must be held if not NULL
 * This routine may not block
 *
 * Additional special handling is required when called from an interrupt
 * (VM_ALLOC_INTERRUPT).  We are not allowed to mess with the page cache
 * in this case.
 */
vm_page_t
vm_page_alloc(vm_object_t object, vm_pindex_t pindex, int page_req)
{
        globaldata_t gd;
        vm_object_t obj;
        vm_page_t m;
        u_short pg_color;
        int cpuid_local;

#if 0
        /*
         * Special per-cpu free VM page cache.  The pages are pre-busied
         * and pre-zerod for us.
         */
        if (gd->gd_vmpg_count && (page_req & VM_ALLOC_USE_GD)) {
                crit_enter_gd(gd);
                if (gd->gd_vmpg_count) {
                        m = gd->gd_vmpg_array[--gd->gd_vmpg_count];
                        crit_exit_gd(gd);
                        goto done;
                }
                crit_exit_gd(gd);
        }
#endif
        m = NULL;

        /*
         * CPU LOCALIZATION
         *
         * CPU localization algorithm.  Break the page queues up by physical
         * id and core id (note that two cpu threads will have the same core
         * id, and core_id != gd_cpuid).
         *
         * This is nowhere near perfect, for example the last pindex in a
         * subgroup will overflow into the next cpu or package.  But this
         * should get us good page reuse locality in heavy mixed loads.
         *
         * (may be executed before the APs are started, so other GDs might
         *  not exist!)
         */
        if (page_req & VM_ALLOC_CPU_SPEC)
                cpuid_local = VM_ALLOC_GETCPU(page_req);
        else
                cpuid_local = mycpu->gd_cpuid;

        pg_color = vm_get_pg_color(cpuid_local, object, pindex);

        KKASSERT(page_req & 
                (VM_ALLOC_NORMAL|VM_ALLOC_QUICK|
                 VM_ALLOC_INTERRUPT|VM_ALLOC_SYSTEM));

        /*
         * Certain system threads (pageout daemon, buf_daemon's) are
         * allowed to eat deeper into the free page list.
         */
        if (curthread->td_flags & TDF_SYSTHREAD)
                page_req |= VM_ALLOC_SYSTEM;

        /*
         * Impose various limitations.  Note that the v_free_reserved test
         * must match the opposite of vm_page_count_target() to avoid
         * livelocks, be careful.
         */
loop:
        gd = mycpu;
        if (gd->gd_vmstats.v_free_count >= gd->gd_vmstats.v_free_reserved ||
            ((page_req & VM_ALLOC_INTERRUPT) &&
             gd->gd_vmstats.v_free_count > 0) ||
            ((page_req & VM_ALLOC_SYSTEM) &&
             gd->gd_vmstats.v_cache_count == 0 &&
                gd->gd_vmstats.v_free_count >
                gd->gd_vmstats.v_interrupt_free_min)
        ) {
                /*
                 * The free queue has sufficient free pages to take one out.
                 */
                m = vm_page_select_free(pg_color);
        } else if (page_req & VM_ALLOC_NORMAL) {
                /*
                 * Allocatable from the cache (non-interrupt only).  On
                 * success, we must free the page and try again, thus
                 * ensuring that vmstats.v_*_free_min counters are replenished.
                 */
#ifdef INVARIANTS
                if (curthread->td_preempted) {
                        kprintf("vm_page_alloc(): warning, attempt to allocate"
                                " cache page from preempting interrupt\n");
                        m = NULL;
                } else {
                        m = vm_page_select_cache(pg_color);
                }
#else
                m = vm_page_select_cache(pg_color);
#endif
                /*
                 * On success move the page into the free queue and loop.
                 *
                 * Only do this if we can safely acquire the vm_object lock,
                 * because this is effectively a random page and the caller
                 * might be holding the lock shared, we don't want to
                 * deadlock.
                 */
                if (m != NULL) {
                        KASSERT(m->dirty == 0,
                                ("Found dirty cache page %p", m));
                        if ((obj = m->object) != NULL) {
                                if (vm_object_hold_try(obj)) {
                                        vm_page_protect(m, VM_PROT_NONE);
                                        vm_page_free(m);
                                        /* m->object NULL here */
                                        vm_object_drop(obj);
                                } else {
                                        vm_page_deactivate(m);
                                        vm_page_wakeup(m);
                                }
                        } else {
                                vm_page_protect(m, VM_PROT_NONE);
                                vm_page_free(m);
                        }
                        goto loop;
                }

                /*
                 * On failure return NULL
                 */
                atomic_add_int(&vm_pageout_deficit, 1);
                pagedaemon_wakeup();
                return (NULL);
        } else {
                /*
                 * No pages available, wakeup the pageout daemon and give up.
                 */
                atomic_add_int(&vm_pageout_deficit, 1);
                pagedaemon_wakeup();
                return (NULL);
        }

        /*
         * v_free_count can race so loop if we don't find the expected
         * page.
         */
        if (m == NULL) {
                vmstats_rollup();
                goto loop;
        }

        /*
         * Good page found.  The page has already been busied for us and
         * removed from its queues.
         */
        KASSERT(m->dirty == 0,
                ("vm_page_alloc: free/cache page %p was dirty", m));
        KKASSERT(m->queue == PQ_NONE);

#if 0
done:
#endif
        /*
         * Initialize the structure, inheriting some flags but clearing
         * all the rest.  The page has already been busied for us.
         */
        vm_page_flag_clear(m, ~PG_KEEP_NEWPAGE_MASK);

        KKASSERT(m->wire_count == 0);
        KKASSERT(m->busy == 0);
        m->act_count = 0;
        m->valid = 0;

        /*
         * Caller must be holding the object lock (asserted by
         * vm_page_insert()).
         *
         * NOTE: Inserting a page here does not insert it into any pmaps
         *       (which could cause us to block allocating memory).
         *
         * NOTE: If no object an unassociated page is allocated, m->pindex
         *       can be used by the caller for any purpose.
         */
        if (object) {
                if (vm_page_insert(m, object, pindex) == FALSE) {
                        vm_page_free(m);
                        if ((page_req & VM_ALLOC_NULL_OK) == 0)
                                panic("PAGE RACE %p[%ld]/%p",
                                      object, (long)pindex, m);
                        m = NULL;
                }
        } else {
                m->pindex = pindex;
        }

        /*
         * Don't wakeup too often - wakeup the pageout daemon when
         * we would be nearly out of memory.
         */
        pagedaemon_wakeup();

        /*
         * A PG_BUSY page is returned.
         */
        return (m);
}

/*
 * Returns number of pages available in our DMA memory reserve
 * (adjusted with vm.dma_reserved=<value>m in /boot/loader.conf)
 */
vm_size_t
vm_contig_avail_pages(void)
{
        alist_blk_t blk;
        alist_blk_t count;
        alist_blk_t bfree;
        spin_lock(&vm_contig_spin);
        bfree = alist_free_info(&vm_contig_alist, &blk, &count);
        spin_unlock(&vm_contig_spin);

        return bfree;
}

/*
 * Attempt to allocate contiguous physical memory with the specified
 * requirements.
 */
vm_page_t
vm_page_alloc_contig(vm_paddr_t low, vm_paddr_t high,
                     unsigned long alignment, unsigned long boundary,
                     unsigned long size, vm_memattr_t memattr)
{
        alist_blk_t blk;
        vm_page_t m;
        int i;

        alignment >>= PAGE_SHIFT;
        if (alignment == 0)
                alignment = 1;
        boundary >>= PAGE_SHIFT;
        if (boundary == 0)
                boundary = 1;
        size = (size + PAGE_MASK) >> PAGE_SHIFT;

        spin_lock(&vm_contig_spin);
        blk = alist_alloc(&vm_contig_alist, 0, size);
        if (blk == ALIST_BLOCK_NONE) {
                spin_unlock(&vm_contig_spin);
                if (bootverbose) {
                        kprintf("vm_page_alloc_contig: %ldk nospace\n",
                                (size + PAGE_MASK) * (PAGE_SIZE / 1024));
                }
                return(NULL);
        }
        if (high && ((vm_paddr_t)(blk + size) << PAGE_SHIFT) > high) {
                alist_free(&vm_contig_alist, blk, size);
                spin_unlock(&vm_contig_spin);
                if (bootverbose) {
                        kprintf("vm_page_alloc_contig: %ldk high "
                                "%016jx failed\n",
                                (size + PAGE_MASK) * (PAGE_SIZE / 1024),
                                (intmax_t)high);
                }
                return(NULL);
        }
        spin_unlock(&vm_contig_spin);
        if (vm_contig_verbose) {
                kprintf("vm_page_alloc_contig: %016jx/%ldk\n",
                        (intmax_t)(vm_paddr_t)blk << PAGE_SHIFT,
                        (size + PAGE_MASK) * (PAGE_SIZE / 1024));
        }

        m = PHYS_TO_VM_PAGE((vm_paddr_t)blk << PAGE_SHIFT);
        if (memattr != VM_MEMATTR_DEFAULT)
                for (i = 0;i < size;i++)
                        pmap_page_set_memattr(&m[i], memattr);
        return m;
}

/*
 * Free contiguously allocated pages.  The pages will be wired but not busy.
 * When freeing to the alist we leave them wired and not busy.
 */
void
vm_page_free_contig(vm_page_t m, unsigned long size)
{
        vm_paddr_t pa = VM_PAGE_TO_PHYS(m);
        vm_pindex_t start = pa >> PAGE_SHIFT;
        vm_pindex_t pages = (size + PAGE_MASK) >> PAGE_SHIFT;

        if (vm_contig_verbose) {
                kprintf("vm_page_free_contig:  %016jx/%ldk\n",
                        (intmax_t)pa, size / 1024);
        }
        if (pa < vm_low_phys_reserved) {
                KKASSERT(pa + size <= vm_low_phys_reserved);
                spin_lock(&vm_contig_spin);
                alist_free(&vm_contig_alist, start, pages);
                spin_unlock(&vm_contig_spin);
        } else {
                while (pages) {
                        vm_page_busy_wait(m, FALSE, "cpgfr");
                        vm_page_unwire(m, 0);
                        vm_page_free(m);
                        --pages;
                        ++m;
                }

        }
}


/*
 * Wait for sufficient free memory for nominal heavy memory use kernel
 * operations.
 *
 * WARNING!  Be sure never to call this in any vm_pageout code path, which
 *           will trivially deadlock the system.
 */
void
vm_wait_nominal(void)
{
        while (vm_page_count_min(0))
                vm_wait(0);
}

/*
 * Test if vm_wait_nominal() would block.
 */
int
vm_test_nominal(void)
{
        if (vm_page_count_min(0))
                return(1);
        return(0);
}

/*
 * Block until free pages are available for allocation, called in various
 * places before memory allocations.
 *
 * The caller may loop if vm_page_count_min() == FALSE so we cannot be
 * more generous then that.
 */
void
vm_wait(int timo)
{
        /*
         * never wait forever
         */
        if (timo == 0)
                timo = hz;
        lwkt_gettoken(&vm_token);

        if (curthread == pagethread) {
                /*
                 * The pageout daemon itself needs pages, this is bad.
                 */
                if (vm_page_count_min(0)) {
                        vm_pageout_pages_needed = 1;
                        tsleep(&vm_pageout_pages_needed, 0, "VMWait", timo);
                }
        } else {
                /*
                 * Wakeup the pageout daemon if necessary and wait.
                 *
                 * Do not wait indefinitely for the target to be reached,
                 * as load might prevent it from being reached any time soon.
                 * But wait a little to try to slow down page allocations
                 * and to give more important threads (the pagedaemon)
                 * allocation priority.
                 */
                if (vm_page_count_target()) {
                        if (vm_pages_needed == 0) {
                                vm_pages_needed = 1;
                                wakeup(&vm_pages_needed);
                        }
                        ++vm_pages_waiting;     /* SMP race ok */
                        tsleep(&vmstats.v_free_count, 0, "vmwait", timo);
                }
        }
        lwkt_reltoken(&vm_token);
}

/*
 * Block until free pages are available for allocation
 *
 * Called only from vm_fault so that processes page faulting can be
 * easily tracked.
 */
void
vm_wait_pfault(void)
{
        /*
         * Wakeup the pageout daemon if necessary and wait.
         *
         * Do not wait indefinitely for the target to be reached,
         * as load might prevent it from being reached any time soon.
         * But wait a little to try to slow down page allocations
         * and to give more important threads (the pagedaemon)
         * allocation priority.
         */
        if (vm_page_count_min(0)) {
                lwkt_gettoken(&vm_token);
                while (vm_page_count_severe()) {
                        if (vm_page_count_target()) {
                                thread_t td;

                                if (vm_pages_needed == 0) {
                                        vm_pages_needed = 1;
                                        wakeup(&vm_pages_needed);
                                }
                                ++vm_pages_waiting;     /* SMP race ok */
                                tsleep(&vmstats.v_free_count, 0, "pfault", hz);

                                /*
                                 * Do not stay stuck in the loop if the system is trying
                                 * to kill the process.
                                 */
                                td = curthread;
                                if (td->td_proc && (td->td_proc->p_flags & P_LOWMEMKILL))
                                        break;
                        }
                }
                lwkt_reltoken(&vm_token);
        }
}

/*
 * Put the specified page on the active list (if appropriate).  Ensure
 * that act_count is at least ACT_INIT but do not otherwise mess with it.
 *
 * The caller should be holding the page busied ? XXX
 * This routine may not block.
 */
void
vm_page_activate(vm_page_t m)
{
        u_short oqueue;

        vm_page_spin_lock(m);
        if (m->queue - m->pc != PQ_ACTIVE) {
                _vm_page_queue_spin_lock(m);
                oqueue = _vm_page_rem_queue_spinlocked(m);
                /* page is left spinlocked, queue is unlocked */

                if (oqueue == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;
                if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                        if (m->act_count < ACT_INIT)
                                m->act_count = ACT_INIT;
                        _vm_page_add_queue_spinlocked(m, PQ_ACTIVE + m->pc, 0);
                }
                _vm_page_and_queue_spin_unlock(m);
                if (oqueue == PQ_CACHE || oqueue == PQ_FREE)
                        pagedaemon_wakeup();
        } else {
                if (m->act_count < ACT_INIT)
                        m->act_count = ACT_INIT;
                vm_page_spin_unlock(m);
        }
}

/*
 * Helper routine for vm_page_free_toq() and vm_page_cache().  This
 * routine is called when a page has been added to the cache or free
 * queues.
 *
 * This routine may not block.
 */
static __inline void
vm_page_free_wakeup(void)
{
        globaldata_t gd = mycpu;

        /*
         * If the pageout daemon itself needs pages, then tell it that
         * there are some free.
         */
        if (vm_pageout_pages_needed &&
            gd->gd_vmstats.v_cache_count + gd->gd_vmstats.v_free_count >=
            gd->gd_vmstats.v_pageout_free_min
        ) {
                vm_pageout_pages_needed = 0;
                wakeup(&vm_pageout_pages_needed);
        }

        /*
         * Wakeup processes that are waiting on memory.
         *
         * Generally speaking we want to wakeup stuck processes as soon as
         * possible.  !vm_page_count_min(0) is the absolute minimum point
         * where we can do this.  Wait a bit longer to reduce degenerate
         * re-blocking (vm_page_free_hysteresis).  The target check is just
         * to make sure the min-check w/hysteresis does not exceed the
         * normal target.
         */
        if (vm_pages_waiting) {
                if (!vm_page_count_min(vm_page_free_hysteresis) ||
                    !vm_page_count_target()) {
                        vm_pages_waiting = 0;
                        wakeup(&vmstats.v_free_count);
                        ++mycpu->gd_cnt.v_ppwakeups;
                }
#if 0
                if (!vm_page_count_target()) {
                        /*
                         * Plenty of pages are free, wakeup everyone.
                         */
                        vm_pages_waiting = 0;
                        wakeup(&vmstats.v_free_count);
                        ++mycpu->gd_cnt.v_ppwakeups;
                } else if (!vm_page_count_min(0)) {
                        /*
                         * Some pages are free, wakeup someone.
                         */
                        int wcount = vm_pages_waiting;
                        if (wcount > 0)
                                --wcount;
                        vm_pages_waiting = wcount;
                        wakeup_one(&vmstats.v_free_count);
                        ++mycpu->gd_cnt.v_ppwakeups;
                }
#endif
        }
}

/*
 * Returns the given page to the PQ_FREE or PQ_HOLD list and disassociates
 * it from its VM object.
 *
 * The vm_page must be PG_BUSY on entry.  PG_BUSY will be released on
 * return (the page will have been freed).
 */
void
vm_page_free_toq(vm_page_t m)
{
        mycpu->gd_cnt.v_tfree++;
        KKASSERT((m->flags & PG_MAPPED) == 0);
        KKASSERT(m->flags & PG_BUSY);

        if (m->busy || ((m->queue - m->pc) == PQ_FREE)) {
                kprintf("vm_page_free: pindex(%lu), busy(%d), "
                        "PG_BUSY(%d), hold(%d)\n",
                        (u_long)m->pindex, m->busy,
                        ((m->flags & PG_BUSY) ? 1 : 0), m->hold_count);
                if ((m->queue - m->pc) == PQ_FREE)
                        panic("vm_page_free: freeing free page");
                else
                        panic("vm_page_free: freeing busy page");
        }

        /*
         * Remove from object, spinlock the page and its queues and
         * remove from any queue.  No queue spinlock will be held
         * after this section (because the page was removed from any
         * queue).
         */
        vm_page_remove(m);
        vm_page_and_queue_spin_lock(m);
        _vm_page_rem_queue_spinlocked(m);

        /*
         * No further management of fictitious pages occurs beyond object
         * and queue removal.
         */
        if ((m->flags & PG_FICTITIOUS) != 0) {
                vm_page_spin_unlock(m);
                vm_page_wakeup(m);
                return;
        }

        m->valid = 0;
        vm_page_undirty(m);

        if (m->wire_count != 0) {
                if (m->wire_count > 1) {
                    panic(
                        "vm_page_free: invalid wire count (%d), pindex: 0x%lx",
                        m->wire_count, (long)m->pindex);
                }
                panic("vm_page_free: freeing wired page");
        }

        /*
         * Clear the UNMANAGED flag when freeing an unmanaged page.
         * Clear the NEED_COMMIT flag
         */
        if (m->flags & PG_UNMANAGED)
                vm_page_flag_clear(m, PG_UNMANAGED);
        if (m->flags & PG_NEED_COMMIT)
                vm_page_flag_clear(m, PG_NEED_COMMIT);

        if (m->hold_count != 0) {
                _vm_page_add_queue_spinlocked(m, PQ_HOLD + m->pc, 0);
        } else {
                _vm_page_add_queue_spinlocked(m, PQ_FREE + m->pc, 1);
        }

        /*
         * This sequence allows us to clear PG_BUSY while still holding
         * its spin lock, which reduces contention vs allocators.  We
         * must not leave the queue locked or _vm_page_wakeup() may
         * deadlock.
         */
        _vm_page_queue_spin_unlock(m);
        if (_vm_page_wakeup(m)) {
                vm_page_spin_unlock(m);
                wakeup(m);
        } else {
                vm_page_spin_unlock(m);
        }
        vm_page_free_wakeup();
}

/*
 * vm_page_unmanage()
 *
 * Prevent PV management from being done on the page.  The page is
 * removed from the paging queues as if it were wired, and as a 
 * consequence of no longer being managed the pageout daemon will not
 * touch it (since there is no way to locate the pte mappings for the
 * page).  madvise() calls that mess with the pmap will also no longer
 * operate on the page.
 *
 * Beyond that the page is still reasonably 'normal'.  Freeing the page
 * will clear the flag.
 *
 * This routine is used by OBJT_PHYS objects - objects using unswappable
 * physical memory as backing store rather then swap-backed memory and
 * will eventually be extended to support 4MB unmanaged physical 
 * mappings.
 *
 * Caller must be holding the page busy.
 */
void
vm_page_unmanage(vm_page_t m)
{
        KKASSERT(m->flags & PG_BUSY);
        if ((m->flags & PG_UNMANAGED) == 0) {
                if (m->wire_count == 0)
                        vm_page_unqueue(m);
        }
        vm_page_flag_set(m, PG_UNMANAGED);
}

/*
 * Mark this page as wired down by yet another map, removing it from
 * paging queues as necessary.
 *
 * Caller must be holding the page busy.
 */
void
vm_page_wire(vm_page_t m)
{
        /*
         * Only bump the wire statistics if the page is not already wired,
         * and only unqueue the page if it is on some queue (if it is unmanaged
         * it is already off the queues).  Don't do anything with fictitious
         * pages because they are always wired.
         */
        KKASSERT(m->flags & PG_BUSY);
        if ((m->flags & PG_FICTITIOUS) == 0) {
                if (atomic_fetchadd_int(&m->wire_count, 1) == 0) {
                        if ((m->flags & PG_UNMANAGED) == 0)
                                vm_page_unqueue(m);
                        atomic_add_int(&mycpu->gd_vmstats_adj.v_wire_count, 1);
                }
                KASSERT(m->wire_count != 0,
                        ("vm_page_wire: wire_count overflow m=%p", m));
        }
}

/*
 * Release one wiring of this page, potentially enabling it to be paged again.
 *
 * Many pages placed on the inactive queue should actually go
 * into the cache, but it is difficult to figure out which.  What
 * we do instead, if the inactive target is well met, is to put
 * clean pages at the head of the inactive queue instead of the tail.
 * This will cause them to be moved to the cache more quickly and
 * if not actively re-referenced, freed more quickly.  If we just
 * stick these pages at the end of the inactive queue, heavy filesystem
 * meta-data accesses can cause an unnecessary paging load on memory bound 
 * processes.  This optimization causes one-time-use metadata to be
 * reused more quickly.
 *
 * Pages marked PG_NEED_COMMIT are always activated and never placed on
 * the inactive queue.  This helps the pageout daemon determine memory
 * pressure and act on out-of-memory situations more quickly.
 *
 * BUT, if we are in a low-memory situation we have no choice but to
 * put clean pages on the cache queue.
 *
 * A number of routines use vm_page_unwire() to guarantee that the page
 * will go into either the inactive or active queues, and will NEVER
 * be placed in the cache - for example, just after dirtying a page.
 * dirty pages in the cache are not allowed.
 *
 * This routine may not block.
 */
void
vm_page_unwire(vm_page_t m, int activate)
{
        KKASSERT(m->flags & PG_BUSY);
        if (m->flags & PG_FICTITIOUS) {
                /* do nothing */
        } else if (m->wire_count <= 0) {
                panic("vm_page_unwire: invalid wire count: %d", m->wire_count);
        } else {
                if (atomic_fetchadd_int(&m->wire_count, -1) == 1) {
                        atomic_add_int(&mycpu->gd_vmstats_adj.v_wire_count, -1);
                        if (m->flags & PG_UNMANAGED) {
                                ;
                        } else if (activate || (m->flags & PG_NEED_COMMIT)) {
                                vm_page_spin_lock(m);
                                _vm_page_add_queue_spinlocked(m,
                                                        PQ_ACTIVE + m->pc, 0);
                                _vm_page_and_queue_spin_unlock(m);
                        } else {
                                vm_page_spin_lock(m);
                                vm_page_flag_clear(m, PG_WINATCFLS);
                                _vm_page_add_queue_spinlocked(m,
                                                        PQ_INACTIVE + m->pc, 0);
                                ++vm_swapcache_inactive_heuristic;
                                _vm_page_and_queue_spin_unlock(m);
                        }
                }
        }
}

/*
 * Move the specified page to the inactive queue.  If the page has
 * any associated swap, the swap is deallocated.
 *
 * Normally athead is 0 resulting in LRU operation.  athead is set
 * to 1 if we want this page to be 'as if it were placed in the cache',
 * except without unmapping it from the process address space.
 *
 * vm_page's spinlock must be held on entry and will remain held on return.
 * This routine may not block.
 */
static void
_vm_page_deactivate_locked(vm_page_t m, int athead)
{
        u_short oqueue;

        /*
         * Ignore if already inactive.
         */
        if (m->queue - m->pc == PQ_INACTIVE)
                return;
        _vm_page_queue_spin_lock(m);
        oqueue = _vm_page_rem_queue_spinlocked(m);

        if (m->wire_count == 0 && (m->flags & PG_UNMANAGED) == 0) {
                if (oqueue == PQ_CACHE)
                        mycpu->gd_cnt.v_reactivated++;
                vm_page_flag_clear(m, PG_WINATCFLS);
                _vm_page_add_queue_spinlocked(m, PQ_INACTIVE + m->pc, athead);
                if (athead == 0)
                        ++vm_swapcache_inactive_heuristic;
        }
        /* NOTE: PQ_NONE if condition not taken */
        _vm_page_queue_spin_unlock(m);
        /* leaves vm_page spinlocked */
}

/*
 * Attempt to deactivate a page.
 *
 * No requirements.
 */
void
vm_page_deactivate(vm_page_t m)
{
        vm_page_spin_lock(m);
        _vm_page_deactivate_locked(m, 0);
        vm_page_spin_unlock(m);
}

void
vm_page_deactivate_locked(vm_page_t m)
{
        _vm_page_deactivate_locked(m, 0);
}

/*
 * Attempt to move a busied page to PQ_CACHE, then unconditionally unbusy it.
 *
 * This function returns non-zero if it successfully moved the page to
 * PQ_CACHE.
 *
 * This function unconditionally unbusies the page on return.
 */
int
vm_page_try_to_cache(vm_page_t m)
{
        vm_page_spin_lock(m);
        if (m->dirty || m->hold_count || m->wire_count ||
            (m->flags & (PG_UNMANAGED | PG_NEED_COMMIT))) {
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                return(0);
        }
        vm_page_spin_unlock(m);

        /*
         * Page busied by us and no longer spinlocked.  Dirty pages cannot
         * be moved to the cache.
         */
        vm_page_test_dirty(m);
        if (m->dirty || (m->flags & PG_NEED_COMMIT)) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_cache(m);
        return(1);
}

/*
 * Attempt to free the page.  If we cannot free it, we do nothing.
 * 1 is returned on success, 0 on failure.
 *
 * No requirements.
 */
int
vm_page_try_to_free(vm_page_t m)
{
        vm_page_spin_lock(m);
        if (vm_page_busy_try(m, TRUE)) {
                vm_page_spin_unlock(m);
                return(0);
        }

        /*
         * The page can be in any state, including already being on the free
         * queue.  Check to see if it really can be freed.
         */
        if (m->dirty ||                         /* can't free if it is dirty */
            m->hold_count ||                    /* or held (XXX may be wrong) */
            m->wire_count ||                    /* or wired */
            (m->flags & (PG_UNMANAGED |         /* or unmanaged */
                         PG_NEED_COMMIT)) ||    /* or needs a commit */
            m->queue - m->pc == PQ_FREE ||      /* already on PQ_FREE */
            m->queue - m->pc == PQ_HOLD) {      /* already on PQ_HOLD */
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                return(0);
        }
        vm_page_spin_unlock(m);

        /*
         * We can probably free the page.
         *
         * Page busied by us and no longer spinlocked.  Dirty pages will
         * not be freed by this function.    We have to re-test the
         * dirty bit after cleaning out the pmaps.
         */
        vm_page_test_dirty(m);
        if (m->dirty || (m->flags & PG_NEED_COMMIT)) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_protect(m, VM_PROT_NONE);
        if (m->dirty || (m->flags & PG_NEED_COMMIT)) {
                vm_page_wakeup(m);
                return(0);
        }
        vm_page_free(m);
        return(1);
}

/*
 * vm_page_cache
 *
 * Put the specified page onto the page cache queue (if appropriate).
 *
 * The page must be busy, and this routine will release the busy and
 * possibly even free the page.
 */
void
vm_page_cache(vm_page_t m)
{
        /*
         * Not suitable for the cache
         */
        if ((m->flags & (PG_UNMANAGED | PG_NEED_COMMIT)) ||
            m->busy || m->wire_count || m->hold_count) {
                vm_page_wakeup(m);
                return;
        }

        /*
         * Already in the cache (and thus not mapped)
         */
        if ((m->queue - m->pc) == PQ_CACHE) {
                KKASSERT((m->flags & PG_MAPPED) == 0);
                vm_page_wakeup(m);
                return;
        }

        /*
         * Caller is required to test m->dirty, but note that the act of
         * removing the page from its maps can cause it to become dirty
         * on an SMP system due to another cpu running in usermode.
         */
        if (m->dirty) {
                panic("vm_page_cache: caching a dirty page, pindex: %ld",
                        (long)m->pindex);
        }

        /*
         * Remove all pmaps and indicate that the page is not
         * writeable or mapped.  Our vm_page_protect() call may
         * have blocked (especially w/ VM_PROT_NONE), so recheck
         * everything.
         */
        vm_page_protect(m, VM_PROT_NONE);
        if ((m->flags & (PG_UNMANAGED | PG_MAPPED)) ||
            m->busy || m->wire_count || m->hold_count) {
                vm_page_wakeup(m);
        } else if (m->dirty || (m->flags & PG_NEED_COMMIT)) {
                vm_page_deactivate(m);
                vm_page_wakeup(m);
        } else {
                _vm_page_and_queue_spin_lock(m);
                _vm_page_rem_queue_spinlocked(m);
                _vm_page_add_queue_spinlocked(m, PQ_CACHE + m->pc, 0);
                _vm_page_queue_spin_unlock(m);
                if (_vm_page_wakeup(m)) {
                        vm_page_spin_unlock(m);
                        wakeup(m);
                } else {
                        vm_page_spin_unlock(m);
                }
                vm_page_free_wakeup();
        }
}

/*
 * vm_page_dontneed()
 *
 * Cache, deactivate, or do nothing as appropriate.  This routine
 * is typically used by madvise() MADV_DONTNEED.
 *
 * Generally speaking we want to move the page into the cache so
 * it gets reused quickly.  However, this can result in a silly syndrome
 * due to the page recycling too quickly.  Small objects will not be
 * fully cached.  On the otherhand, if we move the page to the inactive
 * queue we wind up with a problem whereby very large objects 
 * unnecessarily blow away our inactive and cache queues.
 *
 * The solution is to move the pages based on a fixed weighting.  We
 * either leave them alone, deactivate them, or move them to the cache,
 * where moving them to the cache has the highest weighting.
 * By forcing some pages into other queues we eventually force the
 * system to balance the queues, potentially recovering other unrelated
 * space from active.  The idea is to not force this to happen too
 * often.
 *
 * The page must be busied.
 */
void
vm_page_dontneed(vm_page_t m)
{
        static int dnweight;
        int dnw;
        int head;

        dnw = ++dnweight;

        /*
         * occassionally leave the page alone
         */
        if ((dnw & 0x01F0) == 0 ||
            m->queue - m->pc == PQ_INACTIVE ||
            m->queue - m->pc == PQ_CACHE
        ) {
                if (m->act_count >= ACT_INIT)
                        --m->act_count;
                return;
        }

        /*
         * If vm_page_dontneed() is inactivating a page, it must clear
         * the referenced flag; otherwise the pagedaemon will see references
         * on the page in the inactive queue and reactivate it. Until the 
         * page can move to the cache queue, madvise's job is not done.
         */
        vm_page_flag_clear(m, PG_REFERENCED);
        pmap_clear_reference(m);

        if (m->dirty == 0)
                vm_page_test_dirty(m);

        if (m->dirty || (dnw & 0x0070) == 0) {
                /*
                 * Deactivate the page 3 times out of 32.
                 */
                head = 0;
        } else {
                /*
                 * Cache the page 28 times out of every 32.  Note that
                 * the page is deactivated instead of cached, but placed
                 * at the head of the queue instead of the tail.
                 */
                head = 1;
        }
        vm_page_spin_lock(m);
        _vm_page_deactivate_locked(m, head);
        vm_page_spin_unlock(m);
}

/*
 * These routines manipulate the 'soft busy' count for a page.  A soft busy
 * is almost like PG_BUSY except that it allows certain compatible operations
 * to occur on the page while it is busy.  For example, a page undergoing a
 * write can still be mapped read-only.
 *
 * Because vm_pages can overlap buffers m->busy can be > 1.  m->busy is only
 * adjusted while the vm_page is PG_BUSY so the flash will occur when the
 * busy bit is cleared.
 *
 * The caller must hold the page BUSY when making these two calls.
 */
void
vm_page_io_start(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_io_start: page not busy!!!"));
        atomic_add_char(&m->busy, 1);
        vm_page_flag_set(m, PG_SBUSY);
}

void
vm_page_io_finish(vm_page_t m)
{
        KASSERT(m->flags & PG_BUSY, ("vm_page_io_finish: page not busy!!!"));
        atomic_subtract_char(&m->busy, 1);
        if (m->busy == 0)
                vm_page_flag_clear(m, PG_SBUSY);
}

/*
 * Indicate that a clean VM page requires a filesystem commit and cannot
 * be reused.  Used by tmpfs.
 */
void
vm_page_need_commit(vm_page_t m)
{
        vm_page_flag_set(m, PG_NEED_COMMIT);
        vm_object_set_writeable_dirty(m->object);
}

void
vm_page_clear_commit(vm_page_t m)
{
        vm_page_flag_clear(m, PG_NEED_COMMIT);
}

/*
 * Grab a page, blocking if it is busy and allocating a page if necessary.
 * A busy page is returned or NULL.  The page may or may not be valid and
 * might not be on a queue (the caller is responsible for the disposition of
 * the page).
 *
 * If VM_ALLOC_ZERO is specified and the grab must allocate a new page, the
 * page will be zero'd and marked valid.
 *
 * If VM_ALLOC_FORCE_ZERO is specified the page will be zero'd and marked
 * valid even if it already exists.
 *
 * If VM_ALLOC_RETRY is specified this routine will never return NULL.  Also
 * note that VM_ALLOC_NORMAL must be specified if VM_ALLOC_RETRY is specified.
 * VM_ALLOC_NULL_OK is implied when VM_ALLOC_RETRY is specified.
 *
 * This routine may block, but if VM_ALLOC_RETRY is not set then NULL is
 * always returned if we had blocked.  
 *
 * This routine may not be called from an interrupt.
 *
 * No other requirements.
 */
vm_page_t
vm_page_grab(vm_object_t object, vm_pindex_t pindex, int allocflags)
{
        vm_page_t m;
        int error;
        int shared = 1;

        KKASSERT(allocflags &
                (VM_ALLOC_NORMAL|VM_ALLOC_INTERRUPT|VM_ALLOC_SYSTEM));
        vm_object_hold_shared(object);
        for (;;) {
                m = vm_page_lookup_busy_try(object, pindex, TRUE, &error);
                if (error) {
                        vm_page_sleep_busy(m, TRUE, "pgrbwt");
                        if ((allocflags & VM_ALLOC_RETRY) == 0) {
                                m = NULL;
                                break;
                        }
                        /* retry */
                } else if (m == NULL) {
                        if (shared) {
                                vm_object_upgrade(object);
                                shared = 0;
                        }
                        if (allocflags & VM_ALLOC_RETRY)
                                allocflags |= VM_ALLOC_NULL_OK;
                        m = vm_page_alloc(object, pindex,
                                          allocflags & ~VM_ALLOC_RETRY);
                        if (m)
                                break;
                        vm_wait(0);
                        if ((allocflags & VM_ALLOC_RETRY) == 0)
                                goto failed;
                } else {
                        /* m found */
                        break;
                }
        }

        /*
         * If VM_ALLOC_ZERO an invalid page will be zero'd and set valid.
         *
         * If VM_ALLOC_FORCE_ZERO the page is unconditionally zero'd and set
         * valid even if already valid.
         *
         * NOTE!  We have removed all of the PG_ZERO optimizations and also
         *        removed the idle zeroing code.  These optimizations actually
         *        slow things down on modern cpus because the zerod area is
         *        likely uncached, placing a memory-access burden on the
         *        accesors taking the fault.
         *
         *        By always zeroing the page in-line with the fault, no
         *        dynamic ram reads are needed and the caches are hot, ready
         *        for userland to access the memory.
         */
        if (m->valid == 0) {
                if (allocflags & (VM_ALLOC_ZERO | VM_ALLOC_FORCE_ZERO)) {
                        pmap_zero_page(VM_PAGE_TO_PHYS(m));
                        m->valid = VM_PAGE_BITS_ALL;
                }
        } else if (allocflags & VM_ALLOC_FORCE_ZERO) {
                pmap_zero_page(VM_PAGE_TO_PHYS(m));
                m->valid = VM_PAGE_BITS_ALL;
        }
failed:
        vm_object_drop(object);
        return(m);
}

/*
 * Mapping function for valid bits or for dirty bits in
 * a page.  May not block.
 *
 * Inputs are required to range within a page.
 *
 * No requirements.
 * Non blocking.
 */
int
vm_page_bits(int base, int size)
{
        int first_bit;
        int last_bit;

        KASSERT(
            base + size <= PAGE_SIZE,
            ("vm_page_bits: illegal base/size %d/%d", base, size)
        );

        if (size == 0)          /* handle degenerate case */
                return(0);

        first_bit = base >> DEV_BSHIFT;
        last_bit = (base + size - 1) >> DEV_BSHIFT;

        return ((2 << last_bit) - (1 << first_bit));
}

/*
 * Sets portions of a page valid and clean.  The arguments are expected
 * to be DEV_BSIZE aligned but if they aren't the bitmap is inclusive
 * of any partial chunks touched by the range.  The invalid portion of
 * such chunks will be zero'd.
 *
 * NOTE: When truncating a buffer vnode_pager_setsize() will automatically
 *       align base to DEV_BSIZE so as not to mark clean a partially
 *       truncated device block.  Otherwise the dirty page status might be
 *       lost.
 *
 * This routine may not block.
 *
 * (base + size) must be less then or equal to PAGE_SIZE.
 */
static void
_vm_page_zero_valid(vm_page_t m, int base, int size)
{
        int frag;
        int endoff;

        if (size == 0)  /* handle degenerate case */
                return;

        /*
         * If the base is not DEV_BSIZE aligned and the valid
         * bit is clear, we have to zero out a portion of the
         * first block.
         */

        if ((frag = base & ~(DEV_BSIZE - 1)) != base &&
            (m->valid & (1 << (base >> DEV_BSHIFT))) == 0
        ) {
                pmap_zero_page_area(
                    VM_PAGE_TO_PHYS(m),
                    frag,
                    base - frag
                );
        }

        /*
         * If the ending offset is not DEV_BSIZE aligned and the 
         * valid bit is clear, we have to zero out a portion of
         * the last block.
         */

        endoff = base + size;

        if ((frag = endoff & ~(DEV_BSIZE - 1)) != endoff &&
            (m->valid & (1 << (endoff >> DEV_BSHIFT))) == 0
        ) {
                pmap_zero_page_area(
                    VM_PAGE_TO_PHYS(m),
                    endoff,
                    DEV_BSIZE - (endoff & (DEV_BSIZE - 1))
                );
        }
}

/*
 * Set valid, clear dirty bits.  If validating the entire
 * page we can safely clear the pmap modify bit.  We also
 * use this opportunity to clear the PG_NOSYNC flag.  If a process
 * takes a write fault on a MAP_NOSYNC memory area the flag will
 * be set again.
 *
 * We set valid bits inclusive of any overlap, but we can only
 * clear dirty bits for DEV_BSIZE chunks that are fully within
 * the range.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_set_valid(vm_page_t m, int base, int size)
{
        _vm_page_zero_valid(m, base, size);
        m->valid |= vm_page_bits(base, size);
}


/*
 * Set valid bits and clear dirty bits.
 *
 * Page must be busied by caller.
 *
 * NOTE: This function does not clear the pmap modified bit.
 *       Also note that e.g. NFS may use a byte-granular base
 *       and size.
 *
 * No other requirements.
 */
void
vm_page_set_validclean(vm_page_t m, int base, int size)
{
        int pagebits;

        _vm_page_zero_valid(m, base, size);
        pagebits = vm_page_bits(base, size);
        m->valid |= pagebits;
        m->dirty &= ~pagebits;
        if (base == 0 && size == PAGE_SIZE) {
                /*pmap_clear_modify(m);*/
                vm_page_flag_clear(m, PG_NOSYNC);
        }
}

/*
 * Set valid & dirty.  Used by buwrite()
 *
 * Page must be busied by caller.
 */
void
vm_page_set_validdirty(vm_page_t m, int base, int size)
{
        int pagebits;

        pagebits = vm_page_bits(base, size);
        m->valid |= pagebits;
        m->dirty |= pagebits;
        if (m->object)
               vm_object_set_writeable_dirty(m->object);
}

/*
 * Clear dirty bits.
 *
 * NOTE: This function does not clear the pmap modified bit.
 *       Also note that e.g. NFS may use a byte-granular base
 *       and size.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_clear_dirty(vm_page_t m, int base, int size)
{
        m->dirty &= ~vm_page_bits(base, size);
        if (base == 0 && size == PAGE_SIZE) {
                /*pmap_clear_modify(m);*/
                vm_page_flag_clear(m, PG_NOSYNC);
        }
}

/*
 * Make the page all-dirty.
 *
 * Also make sure the related object and vnode reflect the fact that the
 * object may now contain a dirty page.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_dirty(vm_page_t m)
{
#ifdef INVARIANTS
        int pqtype = m->queue - m->pc;
#endif
        KASSERT(pqtype != PQ_CACHE && pqtype != PQ_FREE,
                ("vm_page_dirty: page in free/cache queue!"));
        if (m->dirty != VM_PAGE_BITS_ALL) {
                m->dirty = VM_PAGE_BITS_ALL;
                if (m->object)
                        vm_object_set_writeable_dirty(m->object);
        }
}

/*
 * Invalidates DEV_BSIZE'd chunks within a page.  Both the
 * valid and dirty bits for the effected areas are cleared.
 *
 * Page must be busied?
 * Does not block.
 * No other requirements.
 */
void
vm_page_set_invalid(vm_page_t m, int base, int size)
{
        int bits;

        bits = vm_page_bits(base, size);
        m->valid &= ~bits;
        m->dirty &= ~bits;
        atomic_add_int(&m->object->generation, 1);
}

/*
 * The kernel assumes that the invalid portions of a page contain 
 * garbage, but such pages can be mapped into memory by user code.
 * When this occurs, we must zero out the non-valid portions of the
 * page so user code sees what it expects.
 *
 * Pages are most often semi-valid when the end of a file is mapped 
 * into memory and the file's size is not page aligned.
 *
 * Page must be busied?
 * No other requirements.
 */
void
vm_page_zero_invalid(vm_page_t m, boolean_t setvalid)
{
        int b;
        int i;

        /*
         * Scan the valid bits looking for invalid sections that
         * must be zerod.  Invalid sub-DEV_BSIZE'd areas ( where the
         * valid bit may be set ) have already been zerod by
         * vm_page_set_validclean().
         */
        for (b = i = 0; i <= PAGE_SIZE / DEV_BSIZE; ++i) {
                if (i == (PAGE_SIZE / DEV_BSIZE) || 
                    (m->valid & (1 << i))
                ) {
                        if (i > b) {
                                pmap_zero_page_area(
                                    VM_PAGE_TO_PHYS(m), 
                                    b << DEV_BSHIFT,
                                    (i - b) << DEV_BSHIFT
                                );
                        }
                        b = i + 1;
                }
        }

        /*
         * setvalid is TRUE when we can safely set the zero'd areas
         * as being valid.  We can do this if there are no cache consistency
         * issues.  e.g. it is ok to do with UFS, but not ok to do with NFS.
         */
        if (setvalid)
                m->valid = VM_PAGE_BITS_ALL;
}

/*
 * Is a (partial) page valid?  Note that the case where size == 0
 * will return FALSE in the degenerate case where the page is entirely
 * invalid, and TRUE otherwise.
 *
 * Does not block.
 * No other requirements.
 */
int
vm_page_is_valid(vm_page_t m, int base, int size)
{
        int bits = vm_page_bits(base, size);

        if (m->valid && ((m->valid & bits) == bits))
                return 1;
        else
                return 0;
}

/*
 * update dirty bits from pmap/mmu.  May not block.
 *
 * Caller must hold the page busy
 */
void
vm_page_test_dirty(vm_page_t m)
{
        if ((m->dirty != VM_PAGE_BITS_ALL) && pmap_is_modified(m)) {
                vm_page_dirty(m);
        }
}

/*
 * Register an action, associating it with its vm_page
 */
void
vm_page_register_action(vm_page_action_t action, vm_page_event_t event)
{
        struct vm_page_action_hash *hash;
        int hv;

        hv = (int)((intptr_t)action->m >> 8) & vmaction_hmask;
        hash = &action_hash[hv];

        lockmgr(&hash->lk, LK_EXCLUSIVE);
        vm_page_flag_set(action->m, PG_ACTIONLIST);
        action->event = event;
        LIST_INSERT_HEAD(&hash->list, action, entry);
        lockmgr(&hash->lk, LK_RELEASE);
}

/*
 * Unregister an action, disassociating it from its related vm_page
 */
void
vm_page_unregister_action(vm_page_action_t action)
{
        struct vm_page_action_hash *hash;
        int hv;

        hv = (int)((intptr_t)action->m >> 8) & vmaction_hmask;
        hash = &action_hash[hv];
        lockmgr(&hash->lk, LK_EXCLUSIVE);
        if (action->event != VMEVENT_NONE) {
                action->event = VMEVENT_NONE;
                LIST_REMOVE(action, entry);

                if (LIST_EMPTY(&hash->list))
                        vm_page_flag_clear(action->m, PG_ACTIONLIST);
        }
        lockmgr(&hash->lk, LK_RELEASE);
}

/*
 * Issue an event on a VM page.  Corresponding action structures are
 * removed from the page's list and called.
 *
 * If the vm_page has no more pending action events we clear its
 * PG_ACTIONLIST flag.
 */
void
vm_page_event_internal(vm_page_t m, vm_page_event_t event)
{
        struct vm_page_action_hash *hash;
        struct vm_page_action *scan;
        struct vm_page_action *next;
        int hv;
        int all;

        hv = (int)((intptr_t)m >> 8) & vmaction_hmask;
        hash = &action_hash[hv];
        all = 1;

        lockmgr(&hash->lk, LK_EXCLUSIVE);
        LIST_FOREACH_MUTABLE(scan, &hash->list, entry, next) {
                if (scan->m == m) {
                        if (scan->event == event) {
                                scan->event = VMEVENT_NONE;
                                LIST_REMOVE(scan, entry);
                                scan->func(m, scan);
                                /* XXX */
                        } else {
                                all = 0;
                        }
                }
        }
        if (all)
                vm_page_flag_clear(m, PG_ACTIONLIST);
        lockmgr(&hash->lk, LK_RELEASE);
}

#include "opt_ddb.h"
#ifdef DDB
#include <ddb/ddb.h>

DB_SHOW_COMMAND(page, vm_page_print_page_info)
{
        db_printf("vmstats.v_free_count: %d\n", vmstats.v_free_count);
        db_printf("vmstats.v_cache_count: %d\n", vmstats.v_cache_count);
        db_printf("vmstats.v_inactive_count: %d\n", vmstats.v_inactive_count);
        db_printf("vmstats.v_active_count: %d\n", vmstats.v_active_count);
        db_printf("vmstats.v_wire_count: %d\n", vmstats.v_wire_count);
        db_printf("vmstats.v_free_reserved: %d\n", vmstats.v_free_reserved);
        db_printf("vmstats.v_free_min: %d\n", vmstats.v_free_min);
        db_printf("vmstats.v_free_target: %d\n", vmstats.v_free_target);
        db_printf("vmstats.v_cache_min: %d\n", vmstats.v_cache_min);
        db_printf("vmstats.v_inactive_target: %d\n", vmstats.v_inactive_target);
}

DB_SHOW_COMMAND(pageq, vm_page_print_pageq_info)
{
        int i;
        db_printf("PQ_FREE:");
        for (i = 0; i < PQ_L2_SIZE; i++) {
                db_printf(" %d", vm_page_queues[PQ_FREE + i].lcnt);
        }
        db_printf("\n");
                
        db_printf("PQ_CACHE:");
        for(i = 0; i < PQ_L2_SIZE; i++) {
                db_printf(" %d", vm_page_queues[PQ_CACHE + i].lcnt);
        }
        db_printf("\n");

        db_printf("PQ_ACTIVE:");
        for(i = 0; i < PQ_L2_SIZE; i++) {
                db_printf(" %d", vm_page_queues[PQ_ACTIVE + i].lcnt);
        }
        db_printf("\n");

        db_printf("PQ_INACTIVE:");
        for(i = 0; i < PQ_L2_SIZE; i++) {
                db_printf(" %d", vm_page_queues[PQ_INACTIVE + i].lcnt);
        }
        db_printf("\n");
}
#endif /* DDB */